[quote=@Shadow Dragon]
What are the limits to the Art power?
[/quote]

As of right now, you can't make any picture that's more than one square foot in size, thus, the door thing wouldn't really work at the moment... and as of right now, you can't make pictures that can actually transform either you OR the enemy. As your art magic improves, so does your canvas size, and you should, eventually, be able to use art magic to temporarily change yourself or an enemy.

As for any sort of hard limits on what things you can draw with this magic, there really aren't any. I might say something like 'that won't do as much as you think', or 'that won't do that', but that's on a case-by-case basis.