Tutorials/Traps

Traps are a common mechanism in multiplayer built by players to kill other players or mobs automatically. The following is a list of basic traps with a short tutorial that often assumes the reader has a working understanding of the basic concepts required to build the trap. Traps are considered a subset of mechanisms.

Overview
Traps are devices designed to trap or damage entities, often referred to as targets. Traps are often made up of 3 components: A lure, a trigger, and the damage source. In a simple landmine, the lure could be a base behind the landmine, the trigger a pressure plate, the trap TNT. Not all traps have a lure, they may rely on chance or something else to lure the target.

Explosive traps
The traps here primarily use TNT to cause harm to the target. When testing explosive traps it may be a good idea to use a different block such as the redstone lamp, which like TNT, is triggered by redstone but it is less likely to accidentally blow up prematurely.

The Trick House Trap
This is a trap that can be used to catch someone while they are out adventuring. You place TNT at various points around their house, prioritizing spots which are behind an input like a button or likely to be set alight by an unsuspecting player, like behind an empty fireplace. To finish it all off, place a few pressure plates near their bed with TNT underneath. If the player dies and respawns, they would spawn on top of the pads and cause an easy kill. Keep in mind that some servers would consider this sort of behavior cheating or griefing.

Another explosive trap is to make a platform in the sky and make it look like a fake base. Place w tripwire hooks and put in redstone all around the base with dispenser walls and fill the dispensers with arrows of poison. It is done!

The End Portal Trap
If you have enough TNT, a dropper, and an input, it can't hurt to pump some TNT into the End Portal. It may be in vain, though, as it is not likely that the TNT would actually be sent back to the overworld.

Bog-standard landmine
The landmine by itself is very inefficient and non-lethal. It damages the landscape and deals little if any damage to players. To make it more efficient, there are many variations players can use:
 * If you want to protect the landscape, you can place 2 water sources at the bottom of the hole. Place a half slab at the bottom as sand/ gravel may quench the water source. This method will reduce the dealt damage, however.
 * This is well disguised next to a door; the player may think it is to open the door.
 * By digging a pit underneath it, the player might fall into it.
 * Try to camouflage the landmine by making it less noticeable, e.g. grow tall grass around it.
 * Concrete powder cannot be used in this design, the concrete powder will harden into concrete upon contacting water and quench the water source.

Instant landmine
If you are getting frustrated of wasted TNT because people run away from your landmine filled with tons of TNT, you should build a landmine that explodes instantly.
 * 1) Dig a 3x3x3 hole in the ground, jump in, and stand on a corner.
 * 2) On center, place a block of dirt and a rail on top of it.
 * 3) On the rail, place a minecart with TNT. Be careful not to push it.
 * 4) Destroy the block under the rail to derail the minecart. The minecart will fall one block lower, this won't really cause any damage unless you accidentally pushed the minecart.
 * 5) Put a dispenser with flint and steel above the minecart like shown.
 * 6) Surround the minecart with TNT, cover it all up, and place a pressure plate on top.

Tree trap
When the player chops down the tree, the TNT will be lit by the observer. The observer can be replaced by a lever and a NOT Gate if you are short on quartz.

Death temple
Create BUD underneath the pressure plate in a desert temple. If a player should try to disarm it, KABOOM! Note that if you use the observer, players might be able to detect it, since the pressure plate won't cover it completely.

The hidden house
This trap is the opposite of a TNT door trap: The TNT is obvious, while the house is hidden. Make a field of TNT extending about 5 blocks into the ground. Place signs all over the field saying: "Find my hidden house." It lures people in twice: the TNT danger, and the hidden house challenge. The problem is that there is no house! Beneath the field are pressure plates which ignite the TNT, leaving no time to escape, as you are in a field of TNT 5 blocks under.

TNT Floor House
Blow up a fake base and kill assailants attacking you! (this can also be used for demolition)
 * 1) Build a base, preferably a half-hidden one, as not to arouse suspicion.
 * 2) Have an iron door as the entrance, with a pressure plate to open it.
 * 3) Below, place a block of TNT, but an extra step you can take is to have a circuit which delays the fuse using repeaters so the target won't retreat as soon as they hear the hisss of the TNT.

If any enemy, mob or player steps on the pressure plate (potential griefers included), they will be blown sky-high!

Explosive house
Griefers love blowing and burning people's houses up. This trap turns the grief onto the griefer.
 * 1) Make a decoy house out of wood and possibly wool.
 * 2) Fill the area under it with TNT and make some "rays" of TNT extend from the house.
 * 3) If a griefer happens to burn the house down, they will probably get a bit more of a bang than they expected!

If you use this for demolition (that is, if you have any fragile buildings to be destroyed), you can set it and wait for somebody else to do the work for you by setting it off unknowingly.

C4 trap
The "C4 trap" is a vertical or horizontal stack of TNT with a button wired to a dispenser with a fire charge in it. The dispenser is placed one block above or below the stack (vertical) or one block next to the stack (horizontal). This usually works better for demolition than for a trap. If you want to use it as a trap, wire a pressure plate to the dispenser. This works similarly to a flaming arrow hitting a stack of TNT from above. This works better than a dispenser shooting TNT, because the "C4" stays in one place. Also, if only two TNT blocks are used, it works well as a disposable cannon, even better on obsidian blocks, but not in a tube. All evidence of the trap is usually destroyed. Note: C4 trap from below does not work very well.

Pitfall traps
These traps primarily use fall damage to harm the target. Some minor variation can make a simple pit much more deadly.
 * Make checkerboard pattern of cacti at the bottom of a pit. Cacti does destroy items, though.
 * To effectively improve the size of your pit without digging a larger area, dig a shallow ring around the top layer of your pit. Fill this area with water so that mobs will be dragged to the center. Note that this will reduce fall damage.

Sand trap
When the target walks on top of the trap, break the bottom block of sand. It is a good idea to disguise the trap by making a house on top of the sand. If you do this, you will probably want to put in carpet so as to not make it so obvious. Some variations:
 * You may be able to get the target to break the sand themselves by making the bottom block valuable.
 * You can automate the trap by attaching a piston to the bottom block of sand. If you want to retract the piston when a pressure plate is pressed, use a NOT Gate. You could also use an observer and a piece of bait to lure in any players wanting a piece of that [whatever valuable block you placed].

Fence trap
Construct a hallway. A diagonal hallway works best. Fence posts should be underneath the path and you should drop the sand or gravel for the floor on the fences. Below the fences, you can have a pit.

This works because when a gravity-affected block falls on a fence post, the block stays as an entity. As a result, a player walking between the fence posts will fall through the sand entities, causing them to plummet. Diagonal hallways make it more likely to fall through the sand without landing safely on a fence post. Keep in mind that the sand is going to look half a block higher than a normal block, but this can easily be covered up. The best part: it does not need to be reset!

Chest pitfall

 * 1) Dig a 2x2 hole until you reach a drop which would ruin any player's day.
 * 2) Place 4 hoppers, one per block on the 2x2 hole, pointing into chests.
 * 3) Build some kind of hall to access the chests below.

This can work in conjunction with other traps. The player drops down into the pit, and at the bottom, they die and their items are sucked into the hoppers for you to use.

Painting trap
This is a very easy to make trap which plays on the old secret passage behind the painting trick. The target may unwittingly decide to check for a secret passage behind the painting. Big mistake.

Fake chunk error
Dig a 16&times;16 hole, preferably in line with real chunks, at least 20 blocks deep. Some inexperienced players may think it is a chunk error and walk in.

Fake water pitfall
Dig a hole (2&times;2 works best) at least 30 blocks deep, the deeper the better. At the bottom place a block of lapis lazuli, a block of blue wool or a block of blue stained glass. Add a false corridor at the bottom to make it look like it goes somewhere. When an unsuspecting player comes across the hole, they may think that there is water at the bottom, jump down and die. Experienced players are less likely to fall for this particular trap but it generally works quite well.

Snowball trap
Load a dispenser with snowballs (or other knockback item), and connect it to a pressure plate. When the target walks across the plate, the dispenser, if aimed correctly, shoots a snowball and knocks the target into the pit. You can also replace the dispenser with a piston.

Piston pit
Place the piston so it pushes the block the signs are on. The player can make up to twelve rows using one piston. Make sure there is a block of empty space at the end of where the piston pushes. Connect the piston to a trigger, such a pressure plate or lever, and when the piston moves it should break the signs and cause the sand to fall along with the target. It is also possible to do this by pushing a line of blocks with torches or buttons on them, which may be slightly cheaper. Alternatively, use a sticky piston connected to a NOT gate which retracts a block with a sign on it, which allows the player to use more than 12 rows.

Fake elevator
Make what is shown in the schematic, a water elevator with water only on the top block. Make sure the hole is 30-40 blocks deep, which is enough to kill the player. It could help to place a lure sign near the 'elevator' saying something like "Do not enter!" You can also make the signs' text something like a floor countdown like "35", "34", "33", etc. so players are more likely to fall for the trap. If they want, you can place hoppers and with chests so you can gather the loot from the victims, but if they really want the drops, they will need a secret passage to the bottom of the pit for collection.

Floating sand pitfall
1. Dig a 3-block deep hole of any size. Make sure it's dirt because you need to put plants below.

2. Place double tall plants in the base of the pit.

3. Put sand on top.

4. Break the double tall plants. Then, dig a pit.

5. Break the double plant, and done. You got a floating sand pitfall.

When the target triggers a block update (by breaking the sand or by other means) they will fall into the pit below.

False-floor trap
A false-floor trap is a variation of a pitfall trap. It works by creating a concealed safe route through the pitfall (which is usually very big) to allow authorized players to pass, while catching unauthorized players or mobs and killing them. It generally works best when there is no way around, forcing the player to pass through the trap. If anyone steps on one of the pressure plates with TNT under it, the TNT will explode causing the whole bridge to collapse! Note: You will need to have something under the TNT, perhaps more TNT or something easily destructible to make sure the TNT doesn't fall and fail to ignite the rest of the TNT.
 * 1) Dig a pit. The deeper and longer the better.
 * 2) Place TNT to build a bridge across the pit. It should be at least 2 blocks wide, preferably more as someone could cheat otherwise.
 * 3) Replace some of the TNT with torches. Read the next step to understand which ones to replace.
 * 4) On top of the torches, place sand or gravel. Try to get across the bridge now by only stepping on the sand. Make sure you can do it, because it will be even harder at the end as you must stay off the edges of the sand.
 * 5) Once you have picked a satisfactory path, cover up the TNT with the same blocks as before.
 * 6) Place pressure plates over all the sand/gravel.

Water traps
Water traps use water to suffocate, trap, or push the target. None of these traps will work on zombies, as they will turn into drowned after drowning, instead of dying. Players who use potions of water breathing will also be unaffected.

Fake water elevator
Make a water elevator using soul sand bubble column, but without an exit at the top. The column will force the unfortunate player upward, where they will be trapped against the ceiling, unable to break their way out because of the fact that blocks break much slower underwater. Cobblestone can be swapped for obsidian. This can also be used reversely, with magma blocks, taking advantage of the fact players cannot swim upwards easily. In both cases, the players may not drown since they're in a bubble column.

Retrieval trap
Create a water current that drags the mobs down under a solid block. The current will hold the mobs under until they drown. The loot from the mobs will float, making the collection hard. If you use this trap to kill zombies, they won't die, but will turn into drowned instead. This trap will also not work on skeletons.

Whirlpool trap
Through clever use of magma blocks, you can pull the target down into water. It should be noted that it's possible to breathe while inside a bubble column, so this trap is not useful for drowning players.

Pufferfish Trap 1
Dig a 1 block wide, 1 block long, 2 block deep pit with a magma block floor. Replace the 4 adjacent blocks to the air block at the bottom with trapdoors (make sure they open towards the magma so the pufferfish don't escape and die) and open them, then put a pufferfish in each one. Fill the pit with water, and add an open trapdoor in the hole, which mob AI sees as a solid block. The magma pulls it down and causes fire damage, while the pufferfish poison and damage the mob (with their spines).

Note: This could be disguised as an elevator to a secret by putting the magma further down.

Resource requirements: 1 magma block, 4 buckets of pufferfish, 4 trapdoors (any), and 2 water buckets.

Lava traps
Lava traps usually use lava to burn the target, or distract them for an easier kill. Note that most of these traps will destroy the loot.

Lava staircase trap
This trap can be handy for players who want to deal with assailants. The player should lure the target into the staircase for this trap to be most effective.

When the target steps on the pressure plate, it will be trapped by the lava running down the staircase. Even if they have Fire Resistance, it will take a long time to wade back up.
 * 1) Dig a standard staircase down a ways. The tighter the space available the better.
 * 2) After a certain distance, plate a stone pressure plate in the staircase. It's suggested to place it so it blends in. In the schematic, a wooden pressure plate is used for visibility.
 * 3) Place redstone dust in an upward trail for a certain distance. Make sure it does not look different from any other part of the staircase.
 * 4) Connect the dust to a dispenser and put a lava bucket inside.

This trap can be expanded to make a handy escape mechanism. If you place the pressure plate on the upward side of the dispenser, the lava will flow down onto anyone chasing you. You could also make a hidden escape at the bottom. Just make sure you have a button to remove the lava.

With some clever piston work, the entire trap could be concealed except the pressure plate. Be wary of stepping on the trap yourself or placing the pressure plate in the wrong location.

There are many variations of this trap, so don't be scared to alter elements of it, especially concerning the direction (descending or ascending), who steps on the trap (you or assailant) and more.

Chest lava trap

 * 1) Build 2 rows of sticky pistons such that are facing each other and the rows are 4 blocks apart.
 * 2) Attach solid blocks to the rows of sticky pistons.
 * 3) Link the rows of pistons to redstone torches.
 * 4) Attach the trapped chest to the redstone torches.
 * 5) Dig a hole below the sticky pistons and fill it with lava.
 * 6) Decorate the area around the trapped chest to attract players!

Lava pit

 * 1) Make a 3x3 pit at least 4 blocks deep.
 * 2) Place lava at the top, ladders in the middle, and water at the bottom.
 * 3) If you get mobs to go into the trap, they will burn in the lava and their drops should go into the water.

Lava door
Make a house, and right inside the front door make a pit with lava. Most players will likely notice the trap and avoid it, so it works only on really careless players.

Trapdoor lava pit
If the target should wander onto the pressure plate, good luck getting off!



Lava filler

 * 1) Make a stone room.
 * 2) Place a pressure plate in the room.
 * 3) Connect the plate to a dispenser with lava in it on the ceiling.

Capture traps
These traps don't actually kill the target. Instead another trap is often used, or the player can come later to kill captured mobs.

Curiosity trap
1.Place a pressure plate on a piece of 3 by 3 flat land.

2. Place 4 iron doors in a way that when you step on the pressure plate, the doors will close, revoking your chance to escape.

3. Place a ceiling that is either blast resistant or unbreakable. Also have an observer under the pressure plate that connects to some TNT so that when a player tries to escape, they will get blown up. This not only traps the player, it also kills the player if they try to escape. You can also replace the observer with a block that blends in with the terrain so that they cannot see the TNT.

Disclaimer: This might work on only inexperienced players because pros can use the parts that are shown to think of what might happen to them if they went in. You may also have a bait like having a dropper that throws out diamonds to lure them over to the trap.

Piston trap
This trap is best for 2-tall tunnels, perhaps inside a friend’s mine. Make sure there is a roof over it, so when the target hits the pressure plate, it cannot escape. When the pressure plate is stepped on, two pistons push up. Note that players will easily be able to break blocks and escape so you probably will want to combine this with another trap.

Door trap
This is a very simple and rather obvious trap that is made by putting a pressure plate in the middle of 4 open iron doors so that the target is trapped inside when they enter. If using this trap against mobs such as skeletons, you don’t have to use iron doors.

Shallow pitfall
Dig a 1-block deep pit at least 5x5 blocks. Place fences on the inside edge. Since fences count as one and one half blocks in height, mobs can walk in, but cannot jump out. Alternatively, line the outside with half-slabs. This can also be combined with a mob grinder, via water currents leading to it. Zombies and Skeletons will take damage from sunlight during the day if the pit is uncovered, making this an effective way to sort out creepers. This design does not capture spiders.

Trapping pool
This trap is designed to trap skeletons and zombies, not to kill them!
 * 1) Dig out a 5x5 square.
 * 2) Dig a 3x3 square 2 layers deep in the center.
 * 3) Place water in each of the corners and in the middle of each side on the top, where the water isn't flowing along the top.

Slime trap
This simple trap targets slimes. When a slime of any size wanders around, it may fall into the hole. Since slimes cannot jump in water, it will not be able to escape. You can come by later and kill all the slimes. If you are not interested in the drops, just leave them into lower slime population. This trap is best on superflat survival worlds where slimes spawn frequently. In that case, water can be obtained in villages.
 * 1) Dig a 4x4 hole three blocks deep.
 * 2) Fill the bottom layer with water, so that it is all still water on the bottom.

Repeater one way
If a redstone repeater is in a 2 block high space, like a tunnel, you will crouch automatically as you walk over it. However, you will not crouch if the repeater is blocking the entrance of a tunnel. However, redstone repeaters are broken instantly when mined, making this trap effortless to escape.

Piston traps
These traps use pistons to harm the target.

Crushing trap
This is ideal at the end of a water flow mob grinder as it minimizes drop losses. The design can be expanded to make a long row.

Honeycomb trap
Connect two sticky pistons to a clock circuit so that they rapidly push a honeycomb block back and forth. If done correctly a player fallen into this trap will be unable to get out. Honeycomb block was chosen because tools do not affect the breaking speed, even with enchantments.

Cake trap
If the target moves too near to the cake, the pistons will trap them and destroy the cake.
 * 1) Dig down two blocks in a flat area and put a piston at the bottom.
 * 2) Dig down two blocks around the piston and put redstone dust at the bottom.
 * 3) Dig down two blocks around the redstone and put pistons at the bottom.
 * 4) Cover everything up with the block(s) of your choice.
 * 5) Place pressure plates in a ring around the center block, above the redstone.
 * 6) Put a cake on top of the center piston.
 * 7) Above the outer ring of pistons, place blocks in the air so there is room to walk under if the pistons are retracted.

Pitfall trap
This device uses pistons to push entities into a pit.

Manual traps
These traps require the player to manually trigger the trap, or perhaps even be the trap.

Grave digging
Ask someone if they could dig down at a spot, perhaps because you lost diamonds there. When they get far enough, cover them with sand or gravel. You can also use lava for a more dramatic death, however, this will destroy their drops as well. This will probably only work on inexperienced players.

Facebreaker trap
If done correctly, the gravel blocks should fall on your target's head, thus trapping or killing him. Hence the name facebreaker. Make sure not to take too long or else the target may escape jumping off the gravel or placing blocks.
 * 1) Make a tower that is at least three blocks high so it will be seen from a distance. This will work best when built in a flat area such as plains or desert. The tower will act as a bait for this trap.
 * 2) Around the tower, dig a pit at least three blocks deep. If you want this trap to be fully automatic, dig the pit at least 30 blocks deep.
 * 3) When the target falls in the pit, drop gravel on the target. If you dug the pit at least 30 blocks deep, this isn't necessary, because most players will die from fall damage anyway.

Ore tower

 * 1) Make a tall watchtower.
 * 2) At the top out of sight, put a bunch of TNT.
 * 3) Make a vertical redstone path to the TNT with a lever to activate it.
 * 4) Put a lure at the top, and ask someone to go get it. When they get to the top, pull the lever.

Other traps
The traps here do not yet fit into any of the other categories.

Spike trap
Materials: a dispenser, a pressure plate and any type of arrows. This trap is not lethal, except to players or mobs with very low health. It could be made to be more of an annoyance if you replace the arrows with tipped arrows with potions such as Slowness, Poison, Weakness, or even fire charge to inflict fire damage.
 * 1) Dig a 1x1x1 hole.
 * 2) Place a dispenser facing up in the hole and fill it with arrows.
 * 3) Place a stone pressure plate on top of the dispenser.
 * 4) If the target steps onto the pressure plate, they will get shot by an arrow.

Slow monologue trap
Use shears to collect spider webs. Then dig a 3 block deep hole placing lava at the bottom and cobwebs on the top layer. Anyone not watching their step could get caught in the web and slowly fall to their death, allowing you to get a few dramatic words in as they die.

Falling minecart
There is a way to 'store' fall damage in a minecart and later have someone take that damage even though they don't actually fall a distance that would make them take damage. You can also search up for a video on how to do this.

Magma Carpet Trap
This trap will probably involve a trip to the Nether. After gathering a fair amount of magma blocks, make a room. Use the magma blocks you have gathered to make the floor of the room, and cover ALL the magma blocks with carpets. When the target walks on to the carpet, they will take damage from the hidden magma blocks, often wondering and unable to figure out where the damage is coming from. If they don't figure out the trap soon enough, they will eventually die or lose a lot of health from fire damage.

One alternative is to make the entrance to the Magma Room two iron doors with pressure plates on the outside but not on the inside, potentially trapping the target inside to burn.

This trap could also be a potential mob farm. When the mob is killed by the fire damage, you can enter the room, most likely by a secret entrance, and by sneaking or wearing Frost Walker boots, claim the mob loot and go back out without taking any damage at all.

Note: This trap will not work on all types of Nether mobs, as they are immune to all kinds of fire damage.

Note: This only works pre 1.16.

Anvil trap
When the target stands on the pressure plates, the doors won't open and while they are confused the anvils will fall on them. They will either be killed or if the anvils don't fall from high enough they get injured. This trap is useful to stop thieves from stealing valuable goods, and exploits the fact that people don't look up.
 * 1) Place two iron doors sideways with redstone torches under them so they stay shut.
 * 2) Set up two pressure plates in front of the doors. The plates shouldn't do anything yet.
 * 3) Run redstone dust from underneath the plates onto the roof of your porch to trigger two pistons.
 * 4) Put an anvil on each extended piston arm, and make sure there is a hole through the porch roof down to the entrance where the target stands.

Command mine
Sick of rebuilding land mines that don't even kill the target? Replace the TNT with a command block with the command ' ' and the command block will instantly kill any entity that touches the trigger! If you use a repeating command block instead of an impulse command block and set "needs redstone" to "always active", you don't need a pressure plate. This trap may be of use only in Creative mode, though.

Arrow trap
By connecting this to a trigger, you can rapidly fire arrows at the target. It is recommended to place this trap in a 1-wide 2 tall tunnel so there is less room to run. You can either place this in the side of the tunnel or shooting down the tunnel. Some variations:
 * Place lava in front of the dispenser to catch the target on fire.
 * You can adjust the repeater, which will change the speed. You can also completely change the clock if you don't have quartz.
 * You could use this to knock the target into a pit.
 * Attach this to a RS-Latch to keep it on until a button is pressed.
 * Use tipped arrows with negative effects to make the trap more dangerous.

Murder holes
Wandering mobs will not be afraid to try and walk on the signs. If they do, they will get trapped. This will not always work, so it is advised to make the deeper part wider.
 * 1) Dig a 2-wide trench down 1 block deep on one side, 3 or more on the other.
 * 2) Place signs on the deeper side at the same height as the shallow side.

Spider trap

 * 1) Find a cave spider spawner, or enable cheats and use  to give yourself one. It is recommended to place a torch to keep it from spawning.
 * 2) Dig a pit under it. It should be at least 5 blocks deep.
 * 3) Place cobweb or something for the spiders to spawn on.
 * 4) Break the torch and allow the pit to fill with spiders. You need to be within 15 blocks for this to work.
 * 5) Get a player to go into the pit.

Wither rose field
Surround your base with a field of wither roses or sweet berry bushes, and leave a block-wide path leading to your base, or make a hidden underground tunnel leading to it. Any hostile mob that walks through the field will take lots of damage, but unless you make the field very large, this trap won't be fatal. This trap works only on mobs and not on players, because players can disarm it quickly with just a water bucket. For added effect, place cobwebs on top of the plants, and if you are using wither roses, plant them on soul sand. This way, the mobs have to spend more time inside the trap, making it more fatal.

Fake Base
1. Build a really high staircase up into the sky. The longer you build, the higher it is, the better.

2. Make a hole into the staircase

3. You can even make yourself look like a noob, which will also give you advantage. When someone notices and walks up, due to the player's view, they will fall through the hole you create, resulting in the target falling to the ground. This trap can even be effective with experienced players, if they don't look carefully.

Fake Base 2
1. Build a water elevator ( using soul sand and water )

2. At the top of the elevator, start building a fake base. Do not use any valuable material because unlike last trap, it will be destroyed completely (unless you want to).

3. In the fake base, connect two tripwire hooks together with string right in the top of the elevator. Using redstone dust to lead around the base from the tripwire, then filling it with TNT.

4. If someone notice a base with a water elevator, they will sometimes attempt trying to go up. After they discovered the TNT behind those walls, they are likely to be gone.

Pufferfish Trap 2
1: Make a somewhat small, square-ish room with a one way door and 2 block thick walls

2: Make 1x1x1 holes in the walls*

3: Add trapdoors on each hole. Make sure that when closed they're on the upper half of a block, not on the bottom

4: Connect the one way door to a redstone signal inverter that is triggered when walked through

5: Then connect the signal inverter to the trapdoors, just make sure it allows for enough room for step 6**

6: Fill each hole with a pufferfish.

7: Make it look attractive to go into!

8: It's done!

When in action, the player will be trapped and the pufferfish will inflate and bounce around the room.

* If you use dispensers and repeaters (See below), you could put the holes 2 or 3 blocks apart so that the water doesn't affect the player much, though it could cover the floor in water source blocks. It'd also make the holes look "decorative"

** You could probably use some hoppers attached to dispensers and fill the hoppers with buckets of pufferfish. Then, invert power to the dispenser. This makes it a renewable trap!

** You could make the dispenser fire twice (fire again after the pufferfish leaves)

Triggers
The traps here are most notable for their trigger and can be connected to many different mechanisms of harm.

Trapped Ore
When someone mines the ore the TNT will explode! Be sure to place the torches before the TNT and to not place any TNT next to a lit torch.

Trapped Ore 2
Use a piston to push a TNT next to a redstone torch when a block is mined. The advantage of this method is that the trapped block does not need have wires right next to it and that it can cover a wider area.

Redstone Mine
Instead of a daylight sensor, you can also use an observer. This trap is good because it is very hard to detect. If you build this above ground, it may seem somewhat out of place, so you should cover the redstone ore with carpet or build it underground. When the target walks on the redstone, it will light up triggering the TNT. A similar trap is achieved by putting a valuable block that the player may want to mine in place of the redstone ore. When the player breaks the block, the daylight sensor, provided there's a light source or clear air above it, will activate.

Furnace Trap
Normally people would expect only chests to explode, so this trigger will surprise them as soon as they loot your furnace. You can replace the furnace with any other container for the same effect. If a griefer loots the furnace the comparator will deactivate and the torch will turn on, blowing the victim to bits!
 * 1) Fill a furnace with coal, iron or food.
 * 2) Put a comparator leading away from the furnace. It should turn on.
 * 3) Place a block in front of the comparator.
 * 4) Place a redstone torch on the block, it should turn off.
 * 5) Create a redstone line from the torch to TNT.

Minecart Mine
When the target rides the minecart, they will trigger the TNT and get blown up. It might help to disguise the detector as doing something else, like switching tracks, opening a door, etc.

Wrong Lever
Place several levers on a wall and put TNT behind it. Place a sign saying something along the lines of, "Which one...," "Don't pull these!," or "Passcode entry." Eventually a player with too much curiosity will come along and pull a lever.

Exploding Bed
Connect a bed next to a BUD, the BUD to some TNT, and cover the whole thing in cobblestone. Then just wait for the player to sleep in it and get blasted sky-high.

Invisible Tripwire
This trap relies on the fact that like end portal, string is invisible from the bottom. Make a room or hallway at least 3 blocks high, and put tripwire in a layer on the third layer up. If the victim jumps, they will trigger the trap. However, if the victim sees the tripwire hooks they will probably mine the block so they don't have to jump.

Chest Bomb
If someone puts something inside the chest, it will go into the hopper, turn on the comparator, and activate the TNT. You could attach the comparator directly to the chest, but it would be more obvious as you can see over chests. Trapped chests are also an option but they can be seen by experienced players. Also, they can be seen more easily with resource packs.
 * 1) Place a chest.
 * 2) Place a hopper underneath the chest.
 * 3) Place a comparator pointing away from the hopper.
 * 4) Place TNT in front of the comparator.

Fishing Trap
It is possible to detonate TNT with a pressure plate and a fishing rod. This method is mostly undetectable; however, it is unstable and prone to premature detonation if you don't have patience.

Proximity Detector
A proximity trap is a player detector paired with an output.

Lures
These traps' primary feature is the way they lure the target into the trap. Note that none of these lures work on mobs.

Dropped Loot
You could drop items such as gold or diamonds near your trap to increase chances that someone will walk into it. This works best if you know someone is coming by. Some tips:
 * It might look too obvious with diamonds, so it could be better to use items like iron bars. You could also try to make it look like someone just died.
 * If you want to get elaborate, you could setup a dropper to periodically dispense an item. It would probably be possible to detect if the item was picked up, perhaps using a weighted pressure plate.

Signs
Signs are very useful for luring new, and sometimes even experienced, players into a trap. Here are some messages which can be good to lure players into traps.
 * "Free Diamonds!" This could be good on a trapped chest, but would only work on newbies.
 * "DO NOT ENTER!" Most players would be tempted to do exactly the opposite, even into a possible trap.
 * "DO NOT PRESS!" If you see a button, you really want to press it. Especially if there is a sign saying not to.
 * "FREE ADMIN!" Like the "free diamonds" example above, this probably works on newbies only.

Chests
Chests, especially when paired with signs, can make a good lure. If you place one inconspicuously in a wooden house, what self respecting griefer would not go and investigate?

Ore Blocks
Ore blocks make an irresistible lure. After all, if you saw a diamond block just sitting there on the ground, would you just leave it there? This lure is good when paired with a BUD trigger.

Fake Mineshaft
Abandoned mineshafts are known for lots of loot. If you trap one, you can pretend to have 'accidentally given away directions' to the mineshaft.

Iron Door
An iron door looks somewhat out of place in a dark cave. If a player sees one, they may be tempted to go inside. Unfortunately for them, there may only be a pressure plate on one side of the door, or a landmine hidden under the plate.

Disarming traps
When faced with a trap, the safest course of action is usually to leave the way you came. If the player really wants to disarm it though, here are some tips:
 * Don't try to trip the trap and run away. Unless you have a really safe way of doing this, the trap is probably designed to prevent you from doing this.
 * Watch out for observers. These can be placed inside walls and under pressure plates as a fail safe.
 * Don't assume it is safe to break redstone. It is usually safer to keep redstone in its current state. If it is off, it might be okay to break it. If it is on, it might be okay to place a redstone torch to keep it on. In very elaborate traps the redstone may blink to check if it is broken, so watch out!
 * TNT in water generally doesn't do much damage. If you have a water bucket, it may be helpful to use it if you think everything is about to blow up.
 * Try to always check for traps. If you see a pressure plate next to an iron door, check for observers below the plate, and break the door and plate, and go in. Another problem is underground traps. For ore traps, check for observers again, break them, and then mine the ore.