I think the main character looks cute. The changing hair and accessories is a neat little way to show a change in gameplay as well. Very similar to how Kirby wears his different hats.
The shading overall is just a little bland looking. I'm not sure if that's what you were going for, but I personally like vibrant colors in sprite art. If this was done stylistically than just ignore this, however the variety of colors is nice.
As for your boss character, I would say that on the left leaf you added highlights next to their hair which would most likely either not have highlights or create a shadow instead. I would try adding the highlight on the other side to line up with the right leaf. You could also try making it a more yellow shade to help with contrast.
The shading overall is just a little bland looking. I'm not sure if that's what you were going for, but I personally like vibrant colors in sprite art. If this was done stylistically than just ignore this, however the variety of colors is nice.
As for your boss character, I would say that on the left leaf you added highlights next to their hair which would most likely either not have highlights or create a shadow instead. I would try adding the highlight on the other side to line up with the right leaf. You could also try making it a more yellow shade to help with contrast.