They're pretty good sprites. But the things I see wrong are this:
* I think the sheet could do without the art on the left. Usually I wouldn't say much about things like that, but since this is a SMM-ish sheet, I think it could do without it. Or if you really want it on there, minimize it to just a single Mecha Koopa since you're showing that it's based from the SMW art. (to save space on the sheet)
* The shading on the fourth frame's hind leg is wrong
* The front sprites's beaks are a little bit off, try experimenting with them until they match the size of the side sprites's beaks
* The eyes when the Blue and Red don't disappear in the real games. (this one isn't important, but I thought I'd let you know)
* It might need some missile sprites, and some laser sprites
But they're not bad though.
* I think the sheet could do without the art on the left. Usually I wouldn't say much about things like that, but since this is a SMM-ish sheet, I think it could do without it. Or if you really want it on there, minimize it to just a single Mecha Koopa since you're showing that it's based from the SMW art. (to save space on the sheet)
* The shading on the fourth frame's hind leg is wrong
* The front sprites's beaks are a little bit off, try experimenting with them until they match the size of the side sprites's beaks
* The eyes when the Blue and Red don't disappear in the real games. (this one isn't important, but I thought I'd let you know)
* It might need some missile sprites, and some laser sprites
But they're not bad though.