Peabody's Improbable History - Richard the Lionhearted - S1.E94

Peabody and Sherman travel to meet King Richard the Lionhearted, who is struggling to live up to his legendary title and win a special noble quest. Despite Peabody's best strategies, nothing seems to work, so Peabody cleverly tricks Richard into using a sword that the king believes is magical. With newfound confidence, Richard succeeds in his quest, though it's Peabody's cleverness, not magic, that saves the day.