The wizard is found at about 1800 feet. He takes far more hits than a normal boss to defeat, but is pretty easy to beat. The greatest hazard is that after he has been hit a certain number of times, the avalanche begins again. However, you can rather easily just bounce off of his head and kill him without too much difficulty.
Beating him twice unlocks a badge which grants you all three companions at the start of your run; it costs 1050.
Beating him three times unlocks the 2000 foot pass, which costs 1400 to unlock.