Choose one type of melee weapon, such as a claw or bite. With that weapon, you are capable of killing any creature with a single strike.
Prerequisites: Str 25, Cleave, Great Cleave, Improved Critical (chosen weapon), Overwhelming Critical (chosen weapon), Power Attack, Weapon Focus (chosen weapon).
Benefit: Whenever you score a critical hit with the weapon you have chosen, the target must make a Fortitude save (DC 10 + ½ your HD + your character level + your Str modifier) or die instantly. (Creatures immune to critical hits can’t be affected by this feat.)
Special: You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a new weapon.
Source: Draconomicon, page 68.