Nature strikes back! New balance. Trees instead of biters.
Mods introducing new content into the game.
Changes to enemies or entirely new enemies to deal with.
a broad idea:
Worms are still vanilla
These worms can be big old trees that throw resin at you.
maybe it would be funny if they move around like the other tree mobs. (only very slowly)
¯\_(ツ)_/¯