At the beginning of each upkeep, if no spells were cast last turn, transform Mondronen Shaman.
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.