S3, E51: Marian casts a spell to make Prince John smarter, but it backfires, creating a strange mist over the river. The mist alters minds: crossing one way grants wisdom, the other causes mental regression. Tuck becomes a genius, while the Vikings grow increasingly foolish. As confusion spreads, strange alliances form. Amid shifting loyalties and unpredictable consequences, everyone must adapt to a world turned upside down by magic.