Fire and Ice (aka The Final Battle) - S1.E26

The witches attempt to destroy Alfea once and for all, but then Bloom returns with the dragonfire. She takes down Icy while the other four take down Stormy and Darcy. In the end, Icy, Stormy and Darcy are sent to a goody goody boot camp while all the other witches go back to clean up Cloud Tower. Red Fountain boys stay at Alfea and they all have Prom together.