Star vs. the Forces of Evil (2015)

S1E5 Monster Arm

Before a Karate tournament, Marco suffers a broken arm. In an attempt to help, Star uses her wand to heal him, but her magic goes awry, resulting in Marco acquiring a sinister, sentient tentacle arm instead. As he navigates the challenges of his new appendage, Marco must come to terms with its unpredictable nature while preparing for the upcoming competition. Star and Marco work together to find a solution, facing both humorous and intense moments along the way as they confront the consequences of magical mishaps.