The Confundus Charm

Cormac McLaggen about to be Confunded in Harry Potter and the Half-Blood Prince (2009)

A charm to confuse and befuddle, the Confundus Charm was used to trick people into thinking something about themselves or their surroundings. The spell can also be used on magical objects with some form of sentience, such as the Goblet of Fire. The Charm came in handy when Hermione wanted to influence the Gryffindor Quidditch team's Keeper trials.