When an enemy within your reach would perform an action that normally draws attacks of opportunity, you gain a primary bite or slam attack (your choice) appropriate for your size (1d6/x2 for a medium creature) that you can use to make the attack of opportunity. You can use your Intelligence, Wisdom, or Charisma in place of Strength to determine the attack and damage.

When you know or have prepared fury guard, you can cast spells that would enhance natural attacks and target your fury guard attack.