Hmmm, I don't like it when you use the C64 palette. It's not that it's not nice or anything, but it makes impossible for me to give you any critiques on your colors because they're not going to be changed. Spec work in general is hard to give feedback on because I don't know what was done because of limitations and what was done because of style.
Yusbird's left leg, for example, seems to be popping out of his belly rather than coming from the other side of his body. I'd say to add a deeper shade between where the attach, but I think it's a limitations thing. Yusbird's shadow also seems rather narrow considering he's so plump.
The rock formation that's farthest to the right seems like it should have the highlights turned around if the light is coming from the moon.
Yeah...