Had a nice illusion room in a dungeon, where only one player was seeing the reality. I pre-prepared the notes, so no extra overhead in the session. That one player was also cursed with not being allowed to speak, but that info was also in the note, so the others didn't know. He tried to warn the others using sharades, and they thought he was cursed with mind control and turned on him, until he could convince them otherwise. That was a really fun round.