Flying drake rats. Super anoying when you build something on mountain.

Its the only mob in game that you cant prevent from attacking you with a ditch as it flys over (slimes can still jump it in swamp/raid -- but usualy you build on trees there)

They can also kill your 2 star pigs if raid happens in meadows.

Second would be tar slimes as i always have to carry poision resistance and fire arrows to deal with them (wasting my inventory slots)