Whenever an opponent casts a spell, Tovolar's Magehunter deals 2 damage to that player.
At the beginning of each upkeep, if a player cast two or more spells last turn, transform Tovolar's Magehunter.
For more information on double-faced cards, see the Shadows over Innistrad mechanics article (http://magic.wizards.com/en/articles/archive/feature/shadows-over-innistrad-mechanics).
Tovolar’s Magehunter’s first triggered ability will resolve before the spell that caused it to trigger. If this causes the player who cast that spell to lose the game, that spell won’t resolve.