To trigger the Werewolf's back face's transform ability, a single player must have cast two or more spells during the previous turn. If multiple players each cast just one spell during the previous turn, the ability won't trigger.

The abilities that transform a Werewolf back and forth look at the entire previous turn, even if the Werewolf with that ability wasn't on the battlefield for some or all of that turn.

Flameheart Werewolf's first ability triggers once for each creature blocking or blocked by it. The ability resolves and deals damage to that creature before combat damage is dealt. If that damage destroys a creature blocking Flameheart Werewolf, Flameheart Werewolf doesn't become unblocked.

Kessig Forgemaster's first ability triggers once for each creature blocking or blocked by it. The ability resolves and deals damage to that creature before combat damage is dealt. If that damage destroys a creature blocking Kessig Forgemaster, Kessig Forgemaster doesn't become unblocked.