Great, up until the volcano boss
I like the style of this, and it's really fun to play. I like the new enemy types in each level, and the progression of difficulty as it goes on. Until the last two volcano levels, that is. The one right before the boss and the boss fight itself both feel like a struggle against the controls rather than a fun challenge. I chose all the upgrades except the helmet and different bomb types, so I've got the default bombs with maxed out stats. I don't know if it's any easier with other types, but with these, even though it's obvious what needs to be done with the boss's first form, it takes like 7 or 8 bombs of trial and error to get the timing and spacing just right; which doesn't leave nearly enough bombs for the second form, unless I'm missing a trick to it. But it doesn't seem like the 2-hit plate maneuver from the other volcano levels works on the boss because there's not enough of a delay, and the time limit doesn't really allow for waiting around for them to cluster together enough to take them out in groups of more than 2. So without any means to get more coins for upgrades, I'm just stuck. I don't know if it's actually impossible with the upgrades I chose or if it's just my skill level as a player. But either way, the game ends there for me, which is disappointing because it's a fun game up until that point. So overall, great job, but some flexibility in the upgrade system would make it more fun for less skilled players.