Otto's Irresistible Dance

When an Otto's irresistible dance spell is placed upon a creature, the spell causes the recipient to begin dancing, complete with feet shuffling and tapping. This dance makes it impossible for the victim to do anything other than caper and prance; this cavorting worsens the Armor Class of the creature by -4, makes saving throws impossible except on a roll of 20, and negates any consideration of a shield. Note that the creature must be touched, as if melee combat were taking place and the spellcaster were striking to do damage.