Age of Heroes
If you are wielding a weapon that inflicts slashing damage (such as a labrys or a sword) and is not a light weapon, you may attempt to decapitate an opponent as a full-round action. A decapitation attempt provokes an attack of opportunity and gives you a –4 penalty to your Active Defense and Shield Defense checks for the remainder of the round, as the swing of the blow puts you off guard. You make one (and only one) attack against your opponent, which is made at a –4 penalty. Your opponent may attempt to evade the blow with Active Defense or Shield Defense if possible and armor may soak some of the damage. If you deal your opponent a grievous wound, you have severed his head and he dies immediately. A decapitate attempt cannot be combined with a coup de grace. Creatures that are not vulnerable to critical hits cannot be decapitated.
Exception: Characters with the Improved Decapitate feat do not provoke an attack of opportunity when making a decapitation attempt, though they still incur the penalty to Active Defense and Shield Defense.