Minecraft Dungeons:Slime

Slimes are bouncy cube-shaped hostile mobs that spawn in certain levels in Minecraft Dungeons

Spawning
Slimes spawn most commonly in the Soggy Swamp. Slimes also spawn within the Redstone Mines, the Underhalls, and the Obsidian Pinnacle.

Behavior
Slimes bounce at you and try to ram into you, and they split when defeated.