Brilliant Mountain Troll
Brilliant Hogwarts Hallway
Girls' Toilets, Hogwarts Castle
Despite their diminuitive intelligence, mountain trolls are exceedingly dangerous. Given this, it is astonishing that Harry Potter and Ron Weasley managed to dispatch one at Hogwarts as mere first-years. Quirinus Quirrell set said troll loose as a distraction during an attempt to steal the Philosopher's Stone.