Nether Reactor

The Nether Reactor is a built structure which, when activated, generates a room of Netherrack (before 0.6.0 Obsidian) (7×17×17) with some openings around the reactor called a "Nether Spire" (unofficial name). It also turns the reactor itself, excluding the core, into Glowing Obsidian. At this point the reactor will begin to spawn various blocks and items, as well as Zombie Pigmen (if difficulty is up)

The Nether Reactor is built with a nether reactor core, 4 gold blocks, and 14 cobblestone, arranged in the configuration above.

The Nether Reactor cannot be used in creative mode.

Behavior
When the Nether Reactor is built and the core activated (by tapping), there will be a Client message that says, "Active!", and it generates a room of Netherrack (7x17x17) unofficially called a "Nether Spire". It destroys any block that happens to be in the way of the room. The blocks that make up the reactor, excluding the core, will turn into Glowing Obsidian

The reactor takes 6 iron, 3 diamond (the core), 36 gold (Four blocks) and 14 cobblestone (the structure) to create.

In addition, it will start spawning various items and blocks. These can be gold ingots, melon seeds, paintings, Glowstone Dust, doors, both types of mushroom, bones, cacti, arrows, sugar cane, bowls, beds, bows, Pumpkin seeds, Nether Quartz and feathers, as well as Zombie Pigmen. Due to this great variety of items, it is advisable to empty out one's inventory beforehand so that no items are missed, other than any weapons used to fight the Zombie Pigmen (unless playing in Peaceful mode). After it burns out, there will be a massive Netherrack structure with multiple floors and many holes in its walls. The bottom floor is hollow (all blocks inside other than the reactor are replaced with air), and the upper floors retain the blocks that were already there (air for an above-ground spire, dirt/stone/etc. for an underground spire). The core is still there, and is reusable. The used core is found in a 3x3x3 obsidian box where the reactor was constructed. When the reactor is active, the core's texture will change to red, and after it burns out, it will change to a blackened texture.

The Nether Reactor only lasts around 45 seconds. During the 45 seconds the Reactor is active, it is easy to escape the room, as it is all Netherrack. Once about 5,10, or 15 seconds have passed, the time sets to nighttime, so left over items in the room can despawn once the Nether Reactor stops.

The Zombie Pigmen who spawn are hostile to the player, and will get hurt in sunlight, unlike the ones in the PC or Xbox versions. Their texture and animations are also slightly different. When a Zombie Pigman is killed it drops 0-1 gold ingots, and 0-1 carrots or 0-1 potatoes as a rare drop (As of 0.8.0).

Conditions

 * All players must be within the spire's area.
 * Must be built on Survival mode.
 * If the reactor is to be activated above water, it must be built at least three blocks above water.
 * The reactor must be built low enough for the spire to fully generate, as blocks cannot be created above cloud level.
 * The player must not be standing on a block below the last layer of the reactor.

Trivia

 * The Reactor does not currently function in Creative mode; this is intended.
 * When building the reactor, if the core is placed but the rest of the reactor is unfinished, text will appear onscreen telling that the pattern is incorrect.
 * Once the reactor is turned on, more text will appear, this time just saying, "Active!"
 * The reactor's structure was originally iron and gold blocks rather than cobblestone and gold, but this was changed due to its cost and the fact that the reactor turns everything into Obsidian except the core.
 * The air blocks in the pattern are not optional. This means the player cannot build the reactor underwater unless you waterproof the air blocks in the pattern.
 * The player can quickly mine some or all of the materials out of the reactor after activation and it will still function. This way the player can recycle the expensive Gold Blocks. Another alternative method is to simply have someone else help mine the blocks right after activation. If they're fast enough, they'll have time to mine all four gold blocks with a diamond pickaxe before they turn to obsidian.
 * If the player constructs the reactor near a world edge and activate it, they will see it turn night.
 * There is an elevation limit for the reactor, above which it cannot be activated.
 * If the player wants to hide the spire produced by the reaction, they must build the reactor deep underground.
 * If you don't want the spire to get "blown up", you can break the active core.
 * If the player mines the active core, the glowing obsidian will not turn into normal obsidian.
 * The spire always generates with the same orientation.
 * If the player builds a reactor around the burnt out core, the spire will generate, but no items or Zombie Pigmen will spawn, the cobblestone and gold blocks do not turn into glowing obsidian, and the core remains in its activated state unless mined, making a netherack farm.
 * The spire makes a good mushroom farm due to the low light levels inside it. Mushrooms spread really quickly when in the spire. It also is very easy to set up a large mushroom farm since the spire is multi-leveled and the reactor gives you many red and brown mushrooms.
 * The low light levels in the spire also make a lot of mobs spawn inside it, so be careful!
 * It takes 36 gold ingots, six iron ingots, three diamonds, and 14 cobblestone to build the nether reactor.
 * The ONLY block the nether reactor can't destroy is the "invisible bedrock" on the world edge, mainly because it breaks the netherrack (obsidian 0.5.0) before it spawns.
 * However, if you inventory edit it into your inventory and place it, the Spire will consume it.
 * Do not put the reactor next to your house and other buildings, since it will destroy them.
 * If a Nether Reactor is manually deactivated, nighttime will be eternal, unless one goes to sleep, but daytime would only last about 20 seconds, and quickly fade back to nighttime. This would also cause hostile mobs to stop spawning (but already spawned hostile mobs will remain). This can be easily fixed by ending the server and starting up again.
 * If you activate a Nether Reactor close enough to the bottom layer of the overworld, it can replace the bedrock with netherrack, giving access to the void in survival mode. This was changed later on. If you do this and you're too near the void, it will say all players need to be near the reactor, even if you are single player mode.
 * The spire has over 25 stacks of netherrack, so it will take a while to mine it all by pickaxes.
 * The Nether Reactor is planned to be replaced by some sort of version-exclusive structure in a future update, possibly in 0.10.0.