Tar pit and Tar Slimes

Similar to water and lava pits, the Tar pit is a naturally generated overworld swamp / nether soulsand valley biome structure.

It's made of tar blocks, oil, mud, coal blocks and coal ore.

New block functions: Tar block or Pitch block is black purple gray green colored a semi-solid block just like soulsand or honey, except entities sink in half way, one full block but stand on the one underneath, making jumping out impossible and walking is a lot slower.

Oil is black a viscous liquid behaving like lava, drowning all living entities, inflicting the slowness effect when inside it, a bucket of Oil can be used to smelt 32 items in a furnace.

Fire burns infinity on the surface of it but doesn't destroy it. New mob: Tar bubble is a black sticky slime mob that pops on contact dealing knockback and inflicting the slowness effect.

It only spawns in tar in the tar pit biome, from the bottom floating up to pop like a gas bubble. It drops a pitch item when killed but not when it pops. 9 Pitch is crafted into a Tar block, and 1 Pitch to craft Fire tipped arrows.

Mobs: Undead mobs don't drown in oil; they just sink to the bottom or get stuck on tar. Any mob unfortunate enough to walk inside gets caught in it forever, unless the player helps it out, short mobs like pigs or chickens get trapped only half a block deep.