Star Vs. the Forces of Evil: Season 1, Episode 5 - ProjectFreeTV

1 - 5: Monster Arm

Marco breaks his arm before a karate tournament. Star uses her wand to fix it, but transforms it into a tentacle arm. As Star tries to find a spell to reverse it, Marco begins to like his new powers associated with the arm. However, the arm harbors an evil sentience that intends to take over the world.