Slime Block

The Slime Block is a transparent block that resembles a Slime. If the player (or any other mob) jumps onto the block, they will bounce on it at a slightly lower height than their original jump. When they land back on the block, they will bounce at an even lower height than the previous bounce, and the cycle repeats until the player or mob is just standing on the block. Slime blocks also cause players to move slower while walking on it. Their speed is comparable to Sneaking, and is slower than walking on Soul Sand. Both players and mobs who fall onto this block will take no fall damage. When attached to pistons, slime blocks can move adjacent blocks under the right conditions.

An interesting quirk of Slime blocks (and the end portal frame and monster spawner) is that they are transparent in their rendering only - unlike all other transparent blocks, they can have torches and redstone placed on them, conduct a redstone current, will suffocate mobs, and more.

Usage
Dropped items move quite fast when in water that is flowing over Slime Blocks (although slower than they do over ice). This is particularly useful for transporting resources using water currents because items will keep sliding on Slime Blocks when they are dropped at an angle, even if water is not placed on top. Due to Slime Blocks not melting, unlike ice, Slime Blocks are a far safer and more efficient alternative. Due to the block's no-fall-damage when landed on, this is good when there are drops in your buildings that can only be reached from falling.

Behavior
Slime Blocks will cause Players and Mobs to bounce at a height relative to the height at which the player/mob fell. If the player is holding the jump key, they will perform a normal jump on contact with the Slime Block. The bounce height quickly deteriorates. A fall of 255 blocks only produces a bounce height of about 50 blocks, while a fall of 50 blocks is a bounce height of 22 blocks. Speed is also taken into account when the player hits the Slime Block. When a player hits "Terminal Velocity" in Minecraft, it means that the player can not travel any faster than he or she is already doing so. You can reach terminal velocity from a few hundred block drop. The maximum jump height is around 57.5 blocks. A fall from 6 blocks would rise a player up to 4 blocks height, while a fall from 3 blocks can rise a player up to 2 blocks height. When a single layer of water is present above Slime Blocks, a fall of 255 blocks only produces a bounce height of 37 blocks.

When being pushed upward by a piston, entities will be shot up high

Placing Carpets, Rails, Trapdoors, Redstone Repeaters or Redstone Comparators on a Slime Block does not stop mobs from bouncing and not taking fall damage. Likewise, placing a Pressure Plate on a Slime Block does not stop mobs from bouncing, but the Pressure Plate will activate. Cake, Slabs, and other half blocks stop the bouncing effect.

Most mobs will bounce off of Slime Blocks except for Chickens, Ghasts, and Bats. Strangely Squid will bounce on Slime Blocks even though that mob normally spawns in water. Occasionally Horses may get stuck on a block when trying to spawn them above Slime Blocks in creative. Items, falling sand/gravel, minecarts and boats are not affected by Slime Blocks. Strangely, the item particles that appear when breaking an item are affected by Slime Blocks.

Slime Blocks are the only block that can be broken at speeds quicker than creative mode in survival without the aid of Haste II from a beacon.

Slime Blocks are one of the slowest Blocks in the game; placing ice under Soul Sand is slower than walking on a Slime Block, but not the slowest the player can go.

Motion by pistons
When a Slime Block is pushed or pulled by a Piston, it will attempt to move in the same direction all adjacent blocks that can be pulled by a sticky piston. These blocks may in turn push other blocks. For example, a Slime Block sitting on the ground will attempt to move the ground block underneath itself, which will in turn have to push additional ground blocks in the direction of motion just as if it were being pushed directly by a piston.

The same occurs when a Slime Block is moved by an adjacent Slime Block. For example, a 2×2×2 cube of Slime Blocks may be pushed or pulled as a unit by a single piston acting on any of the blocks in the cube.

A Slime Block adjacent to a block that cannot be moved by pistons will ignore the immobile block. But if an adjacent block could be moved but is prevented by the presence of an immobile block, the Slime Block will be prevented from moving.

Slime Blocks are not pulled by a non-sticky piston, nor are they moved if an adjacent (non-Slime) block is moved by a piston.

The maximum of 12 blocks moved by a piston still applies. For example, a 2×2×3 collection of Slime Blocks may be pushed or pulled by a sticky piston as long as no other movable blocks are adjacent to it.

A piston cannot move itself via a "hook" constructed of slime blocks, but self-propelled contraptions can be created with multiple pistons.

Trivia

 * Translucent blocks (blocks with two different transparencies), such as slime blocks, are now able to be implemented due to a new rendering system.
 * Slime Blocks can be mined instantly with your hand.
 * A Minecart leaving a rail onto a Slime Block will be able to continue on a rail on the opposite side, if it has sufficient momentum leaving the initial rail.
 * Because Chickens tend to land softly, they rarely if ever will bounce on the block.
 * Because it lets light pass through, a Slime Block doesn't deactivate a Beacon.
 * Any entity landing on the sides of the block will not bounce. In order to bounce, you need to land in the middle.
 * The texture of the inside block uses the 10x10 center of the 16x16 slime.png file.
 * Slime blocks under Soul Sand will make you go as slow as ice under Soul Sand.
 * Slime blocks will allow spawning of mobs.
 * A piston moving a slime block horizontally or vertically lanches all entities hit by the block a large distance, except Ender Dragons, item frames and paintings. This can be useful for arrow and TNT cannons or as replacements for elevators.