Really good.
This is really good, the music was beautiful and fit perfectly, and I enjoyed the art style.
My only criticism is that I couldn't quite understand what the motive of the bad guy was. I assume he just wanted the green guys to not have it anymore, but why would he give the guy the artifact only to want it back? Yeah I guess he tried to convince him that it was powerful and worth money, but if that's the case why wouldn't he keep it for himself? I'm sure you have an idea in your head what was going through his mind, but in animation it's important to make sure the audience understands it just as well as you do.
Otherwise, keep making these, I'm sure you'll only get better :)