Tearing Wounds (3.5e Maneuver)

''As the party battled the tarrasque, you noticed a bleeding gash on its underbelly. Before it sealed closed you lept up, grabbing the ragged edges of the wound, and disembowled the titanic beast!''

You make a melee attack. If you hit you do not deal your normal damage, but instead deal damage equal to the enemy's maximum hit points minus their current hit points.

For example if the opponent currently has 10 points of damage, you deal 10 damage. If it has 100 damage, you deal 100 damage. If the opponent is uninjured, you deal no damage. So long as you deal at least 1 point of damage, you aggravate the pain. In addition, the enemy takes a -4 penalty to attack rolls, ability checks, and skill checks from the agonizing pain. This penalty lasts until the creature is fully healed.

This maneuver requires you to get up close and personal, entering the opponent's space and triggering an attack of opportunity as normal.