Use Magic every chance you can get, and always use 1 magic power up at a time (holding the magic button ranges from 1 to more magic). Pretty much every time a magic dropped I'd pick it up, and then use it to make the mages drop more magic for me.
If you die, you come back with magic, so feel free to keep dying just to get that 1 extra magic. If you don't die, this should take 2-3 levels. But I was able to get it by the end of the first by farming deaths.