You need to find 10 Trollfaces in 10 seconds. If the timer runs out, you lose. To win, find the 10 trollfaces before the timer runs out. You may be thinking, "Where is the tenth trollface?" It's on the level failed screen, press it to win, but make sure you've pressed the other 9 first.

Troll Control is an optional Side Quest in Hogwarts Legacy that you'll receive after speaking to the Brocburrow resident, Alexandra Ricketts.