The Mewtwo thing with the Lati wings was saved as a JPEG. You obviously figured out not to do that, since your other sprites are PNG, but re-saving the sprite as PNG doesn't fix the JPEG damage.
On your revamps, you just recolored. You need to customize the shading so that it looks like a newer sprite. You also left the outlines completely black. You need to shade them like a newer sprite; use the new one for reference.
Your mixes are pretty much just cutting, pasting, and recoloring. You should change the shading and outlining on the added parts so that they look like they fit with the new base sprite.
Your recolors aren't bad, but you should probably change some of the shading and outlining when you recolor so that it fits better with the sprite's new set of colors.