Devastating Critical( Epic Level Handbook, p. 53)
Choose one type of melee weapon, such as longsword or greataxe. With that weapon, you are capable of killing any creature with a single strike.
Cleave (PH) , Great Cleave (PH) , Improved Critical (PH) (weapon to be chosen) , Overwhelming Critical (ELH) (weapon to be chosen) , Power Attack (PH) , Weapon Focus (PH) (weapon to be chosen) , STR 25,
When using the weapon you have selected, whenever you score a critical hit the target must make a Fortitude save (DC 10 + 1/2 your character level + your Strength modifier) or die instantly. (Creatures immune to critical hits can't be affected by this feat.)
You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a different type of weapon.