Well, I dunno if it's still early boss or not, But I can't beat the mushroom boss? cz, the area of walkin' is too small for me. well, tonight I want to play it again. (Just thinking a new way to beat it). and yeah, I tried fight each monster in new area, and back to the save point (so I just only beat the boss later) BUT... when I go back. the monsters back too! (Hahahaaaaaah...)
Ah yes. The mushroom mini boss is a definite difficulty spike. I'd suggest moving in the small opening space of the fight kinda slowly, and trying to take out the greenie on the left as quickly as possible, to open up more movement space. The good news is, you'll only have to beat him once. Thanks again for the feedback!