Magma Cube

A magma cube is a hostile mob whose skin is dark red and black with red, orange, and yellow eyes. It is found in big, small, and tiny sizes, exclusively in the Nether. They are considered the Nether equivalent of slimes, with similar behaviors.

Spawning
They are found in some Nether places at all light levels. The space they spawn in must be clear of solid obstructions and liquids.

Big magma cubes require a 3×2½×3 space to spawn, small magma cubes require a 3×2×3 space, and tiny magma cubes require a 1×2×1 space (or 1×1×1 if the upper block is not opaque).

Magma cubes' size is affected by regional difficulty: chances range from 33% for each size at the low difficulty to 16% small, 33% medium, and 50% big with higher difficulty.

Nether Wastes
Magma cubes spawn uncommonly in nether wastes in groups of 1 to 4.

Nether Fortresses
Magma cubes spawn commonly in fortresses groups of 1 to 4.

Basalt Deltas
Magma cubes spawn commonly in basalt deltas groups of 2 to 5.

Spawners
Magma cube spawners generate in the treasure room of bastions.

Drops
for big magma cubes, for small and  for tiny.

Large and small magma cubes drop 0-1 magma cream. The maximum can be increased by 1 per level of Looting. Tiny magma cubes drop nothing.

Behavior
A magma cube moves by hopping at intervals of 40 to 120 ticks (2 to 6 seconds).

A magma cube seeks out any player or an iron golem within a 16 blocks spherical distance. If it finds no enemy, it waits for 40 to 120 ticks (2 to 6 seconds), then changes direction by a random amount up to 57.30° (1 radian) left or right, jumps, and repeat the process. If it finds a target, the delay before jumping is $1⁄3$ as long (13 to 40 ticks) and the magma cube changes direction directly toward the target before jumping.

Magma cubes cannot be hurt by fall damage or burning, and are not slowed down by lava. They can swim upward in lava and leap above its surface.

They avoid water, can swim, and don't drown.

Their jump height depends on their size. Their forward speed is twice that of most other mobs. They always make a distinct sound upon jumping up and landing, but no idle sounds.

When a magma cube is killed, it split into 2-4 smaller magma cubes. Tiny magma cubes disappear when killed, like other mobs.

Unlike most mobs, magma cubes have no pathfinding ability, meaning that they do not avoid falling off cliffs and cannot go around walls, even when chasing a player.

"Few are as deadly as the Magma Cube locking sights on you. Get seen by this red and black horror and it bounces for you relentlessly, its springy body barely concealing a molten lava core that will fill your body with hot flamy pain. Friendly hugs are not advised."

- Tom Stone

Combat
Magma cubes attack by jumping and attempting to land on the player, and cause damage when touched anywhere. As their jump rate is random, magma cubes can be hard to fight.

The health of a magma cube is its size squared; the attack strength is its size + 2, and the armor points are its size tripled.

A magma cube jumps a distance of approximately its length times 1.5 and a height equivalent to its size in blocks. This means that a large magma cube jumps 4 blocks in height and moves significantly quicker than a small magma cube, which jumps 2 blocks in height; while a tiny magma cube moves slowly and jumps 1 block in height.

Magma cubes have an attack speed twice as fast as most mobs. Mobs like zombies attack once per second, while magma cubes attack twice per second. This means that a large magma cube deals of damage per second on normal difficulty.

Data values
Magma cubes have entity data associated with them that contain various properties of the mob.

Trivia

 * When a larger magma cube that has a name dies, the smaller magma cubes it spawns also have the same name, just like slimes.