In some versions, Otto’s also causes the target to provoke attacks of opportunity on their turn (because they’re dancing). If you can land this spell on the Big Bad for even one round, you basically give all of your melee characters an extra attack. Not only that, but it also drastically reduces the victim’s defenses…

The reason Otto’s Irresistible Dance is 8th Level is because it doesn’t allow either a saving throw or magic resistance. No matter how powerful your opponent is (Draco-Lich, Demi-God, Squirrel Girl) you take them off the board for 2-5 rounds- rounds where they can’t hurt you, heal their minions, or teleport away.