Thanks for your feedback! For real, though, the reason why I didn't put any checkpoint is because I didn't think of how difficult this game would be for new players.
As for the circle death effect, I'm not sure what you are talking about. Every enemy has the same dithering out effect when they dies. It's just that the cave is mostly dark so the dark enemies' death are less noticeable. The circle effects are for the white enemies' projectiles.
By the way, the reason why I use a Henry Stickmin character as my protagonist is simply because I don't want to spend much time designing my character. If I'm going to make a full game, I definitely will create an original character. In this case, what appearances and personalities should this character have?