Executioner

You have been trained in the ancient art of humanely ending a creature's life. You gain the following benefits:

Ability Score Improvement. Your Strength score increases by 1, to a maximum of 20.

Execution. You may use your action to attempt to humanely end the life of a creature lying prone or restrained in front of you. You make your attacks as normal, but damage from all attacks that are nonmagical become slashing, a hit deals double damage, a critical does quadruple damage, and your attacks bypass resistance to slashing damage. Attacks deal critical hits with rolls of 18-20, and on a roll of 20, you decapitate the creature as if you were wielding a vorpal sword. Once you use this feature, you can't use it again until you finish a long rest.