I found the 2nd one to be quite difficult because I made a brain fart and forgot to use my immediate surrounding to my advantage. The fight took forever and the boss ended up leveling a whole forest lol.

3rd one is extremely resistant to most damage, but what kills you is the environment.

4th one was the easiest for me, I think she got bugged tho and din't work as intended...

I go into every new boss without watching let's plays or stuff like that to make it more challenging, they're all "easy" when you understand their patterns and weaknesses.