I know I'm a bit late on this one, but I'll give my 2 cents anyway (hope you don't mind).
I always associate the magician to self-esteem and being able of doing what we want, with everything life has given us so far, our experience, etc.
In this case, I have the feeling that the magician feels like taking a chance on creating a mouse, even when a real mouse is standing right in front of him. The magician doesn' look malicious, or evil, so I think he's doing it for good, not because he feels more powerful through it. But at least he knows he can do it.
And to me, that's what the Magician is all about it, the feeling of doing things, achieving something, even if it's just for the pleasure of achieving, and the act has no particular consequences - good or evil.
I think that, no matter how much we think good or bad about a situation, there's nothing like reality - the big mouse...
ok, hope it made sense...
anjo