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.

If you have no cards in hand after Sage of Ancient Lore enters the battlefield, it will be put into your graveyard before its first triggered ability resolves. You'll draw a card, but Sage of Ancient Lore will already be gone.

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.