Tar Pit

Tar Pits are dangerous Structures, completely made from Tar. They spawn somewhat commonly inside pits in swamp biomes. They are somewhat like lava pools.

It is essentially a death trap as Tar damages the player and it is impossible to escape once you fall in, making it by far the most dangerous naturally occuring mod Structure. Any item that falls into the pit will despawn.

Mobs can walk into Tar Pits and slowly die as their AI doesn't detect that Tar is harmful.