Monsters, Inc. (2001)

In Monstropolis, monsters scare children to generate electricity. Sully, a top scarer, accidentally lets a little girl into their world, turning his life upside down. Along with his friend Mike Wazowski, Sully embarks on a comedic and thrilling quest to return her home. Their journey uncovers a life-changing discovery that could alter the fate of both the monster and human worlds.