Slime Block

The Slime Block is an upcoming, transparent block that resembles a Slime. If the player (or any other mob) jumps onto the block, they bounce on it at a slightly lower height than their original jump. Then when they land back on the block, they bounce at an even lower height than the previous bounce, and the cycle repeats until the player is just standing on the block. The block will be introduced in the Minecraft 1.8 version for PC. Such blocks are now able to be implemented due to a new rendering system. Slime blocks also causes players to move slower while walking on it. Their speed is comparable to Sneaking, and is slower than walking on Soul Sand. Walking on a Slime Block with cake, slabs or carpet over it will retain the slowing effect. Both players and mobs who fall onto this block will take no fall damage.

As a crafting ingredient
A Slime Block can be crafted back into 9 Slimeballs, making it useful as a storage block.

Behaviour
Slime Blocks will cause Players and Mobs to bounce at a height relative to the height at which the player/mob fell at. Items, falling sand/gravel etc. will not be affected by Slime Blocks.

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

No matter the height that a player falls, if they are holding down the jump key, they will perform a normal jump on contact with the Slime Block. Without doing this, you will jump up at most 60% of what you fell.

Trivia

 * Before Snapshot 14w02b, Slime Blocks were known as "Bouncy Blocks" as their real names had not been announced yet.
 * The bounce height quickly deteriorates. A fall of 250 blocks only produces a bounce height of about 50 blocks, while a fall of 50 blocks is a bounce height of 25 blocks.
 * 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.