After you solved all 50 A puzzles, the game gave you the code to visit "Another World" and the evil sorcerer unlocked.

In Puzzle Mode, Select 1-A, after 2-A, all the way to 5-A. After finish the last puzzle in 5-A, you'll get the cheatcode and the end credits. Then restart you DS and you'll be able to play as the Evil Sorcerer.