Slime Block

"Slime blocks can be used to bounce on, like some sort of snot-coated trampoline. The height of your bounce is relative to how far you fall onto the block. So if you say, fall six blocks of height and land on a slime block, you'll bounce four blocks high into the air! Wheeeeee! While this is a lot of fun, it does also mean your feet touched a slime block. You might want to burn those shoes. And those feet. Better safe than sorry."

- Tom Stone

A slime block is a transparent block that mobs can bounce on.

From block loot
Slime blocks can be broken instantly, regardless of held items.

Info
Landing on a slime block does not cause fall damage unless the player is.

Slime blocks are also slightly slippery, but less so than ice.

Slime blocks cause movement on top of them to slow down.

Bouncing
A player or mob that falls onto the top of a slime block bounces to a height proportional to the falling velocity. The bounce height quickly deteriorates. For example, a fall of 255 blocks produces a bounce height of about 50 blocks, while a fall of 50 blocks results in a bounce height of 22 blocks. The maximum bounce height is 57.625 blocks. Entities hitting the side of a slime block do not bounce.

A player holding the key performs a normal jump on contact with the slime block without taking fall damage. A player holding does not bounce at all, and takes fall damage. Landing on the edge of a slime block that is bordered by anything (including air) other than another slime block is treated like landing on a solid block, receiving fall damage and not bouncing.

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 still activates. Cake, slabs, and other half-blocks stop the bouncing effect.

Most mobs bounce off slime blocks except for chickens, ghasts and bats. Occasionally a horse may get stuck on a block when a player tries to spawn it on top of a slime block in Creative mode. Items, falling sand/gravel, minecarts and boats do not bounce on slime blocks. Particles, however, do bounce.

Pistons


When being pushed by a piston, entities (except ender dragons, item frames and paintings) that are ahead are launched into the direction the block is pushed into. When pulled by a piston, no entities are launched.

When a slime block is pushed or pulled by a piston, it attempts to move all adjacent blocks in the same direction. The types of blocks that can be moved are the same as those that can be pulled by a sticky piston. Blocks that cannot be pulled by a sticky piston (i.e. all the blocks listed on the table on the pistons page) stay in place. The blocks that are moved may in turn push other blocks. For example, a slime block sitting on the ground attempts to move the ground block underneath itself, which push additional ground blocks in the direction of motion just as if it were being pushed directly by a piston.

Glazed terracotta and honey blocks are exceptions; they do not move when adjacent slime blocks are moved.

When the adjacent block that is moved is also a slime block, that block attempts to move all its adjacent blocks. 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 ignores the immobile block. However, if an adjacent block could be moved but is prevented by the presence of an immobile block, the slime block is also prevented from moving. This includes slime blocks being pulled rather than pushed, in which case the piston retracts without pulling anything. Liquids are an exception: they aren't moved, but neither do they stop a piston from pushing or pulling blocks into their space (usually destroying the liquid, and in a rare case displacing it through the piston).

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 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.

Sounds
Java Edition:

ID




Trivia

 * Translucent blocks (blocks with two different transparencies), such as slime blocks, are now able to be implemented due to a new rendering system.
 * A minecart leaving a rail onto a slime block can continue on a rail on the opposite side, if it has sufficient momentum leaving the initial rail.
 * Slime blocks under soul sand make the player move slower than if the player was just walking on soul sand. This is also apparent with ice.
 * Rabbits do not jump while on a slime block.
 * Entities launched upward by a slime block on top of a piston achieve slightly more than 6.4 blocks of lift, including the lift from the piston. Entities launched sideways across normal blocks or air are moved 3.510 blocks in the direction of the launch.
 * While falling, placing a slime block while just before impact prevents all fall damage.