You have multiple encounters with trolls. Find a Spongify tile and shoot Spongify at it. Wait for the troll to run at you. Then, jump on the tile towards the troll. He will hit the tile then hit himself on the head.
Get to the nearest Spongify tile and get on it. Then, target it and charge up the Spongify charm. Wait for the troll to start the attack, then release the charm.
