Neat little game but overall I'd agree with the other comment that there's nothing especially fun here. Could use an extra mechanic or two that people would see in a trailer or screenshot and think "I want to do THAT." Some kind of flashy parry or stun or super move or execution sequence. Otherwise, leaning more into the comedy could work too. It is wacky to fight a killer whale, but it doesn't really do anything wacky or silly. You could go in a Parodius kind of direction, or maybe even have silly parodies of well-known bosses and attacks in the genre. A burping mushroom just doesn't really do it for me
Nitpicks:
I kept trying to hit the whale from above when it did its left-right leap, and I could only sometimes hit it from below, never above. You could maybe expand its hurtbox to make that easier
Slime seemed a bit too basic when tackled safely, but you probably know that
It seemed like I couldn't jump over the mushroom's clouds? Maybe you're supposed to dash through them, but I expected jumping to work
I don't understand why the cannonballs still one-shot you while they're sinking in the water (also why do they take so long to sink?)
I quit on the ship fight after losing 1 hit away from beating it. (I moved down too fast after jumping the third fire line, trying to set up for a jump over the next one) (Why does everything one-shot you here? Surely they could 2-shot you instead)