Personally, I enjoy brutally difficult games, though this project doesn't seem to be going that direction, so its probably best to split it up into 2 enemies (Perhaps one with the gun, and one that jumps, and both get the headbutt). I like the idea of a miniboss that takes a simpler enemy archetype and gets some extra moves and health, (perhaps even a move that normal enemies don't get!) I'd eat that up.
Wouldn't mind that being a normal thing for each area either, and now I'm just thinking about how cool a slime miniboss that launches slime everywhere when it lands would be.