It's the difference in AI:
- the Rams run away and then charge once they're far away enough
- the Skulls try to maintain a particular distance (just far enough to dash to) while avoiding their surrounding enemies
- there are some skulls that group together and follow the player closely and seem to have a smaller hitbox - that's the glitch I wrote about, they should have a bug sprite not a skull
- then the fish stick near the bottom and slowly try to get underneath the player
So, I assume you were dealing with a Ram, and yeah I agree that it's annoying because that's how I usually die. But I made it that way so you can't just stand still and click everything around you. I figured they'd make you move around more.