Pinky and the Brain (1995)

S4E1 Brainwashed Pt. 1: Brain, Brain, Go Away

In Washington, DC, Pinky and the Brain find themselves captured by a mysterious entity. During the ordeal, Brain suffers from amnesia, and the duo ends up trapped in a bizarre town where the inhabitants are compelled to carry out the Schëerskåhøvên ritual, which is leading to a nationwide decline in intelligence.