I have seen something with a similar setup, a fire/thunder rotation link. His biggest fault is of his lack of arrows, replaced by the move (with his down taunt animation) that changes the element. It would be better if you mapped the devil-angel move to a taunt, so he still has all of his tracks.
Other than that, this is going to be great!
That was an extremly early beta that I didn't finish cause there was no frame speed command at that time. The character wasn't supposed to play like Link, in fact I planned to remove all projectiles. Also I don't like the idea of adding functionality to taunts, the character should still feel like a smash character and in smash taunts are just taunts. (besides Kirby and Luigi but those doesn't really effect gameplay)
you're sure it's possible to make Marth slow, and make him fast by switching to angel?
You can change the framespeed of each move based on the variable but the attributes will stay the same for both forms since I highly doubt there's a command that changes attributes.
The only concerns I have is that it could easily go over the file size limit.