Nicely done! The composition is really cool; you have two good focal points, and it creates like a hierarchy of power or something. The animation is a great touch as well ^^
I really like how you used the colors! I think it's totally fine being more than 16 colors. I was going to recommend more anti-aliasing but I think that's just a style choice (and maybe to save time since this was indeed a big piece with a lot of texture haha). Maybe dithering the clouds to make them smoother would help? idk :)
Anyway, this is really great art! Happy Pixel Day!!