Death Strike

Assassin. Make one weapon attack against a creature that is surprised, restrained, unconscious, unaware of you, or unable to see you. On a hit, the target takes an extra 12d10 weapon damage and must make a CON save or be stunned until the end of your next turn.

This power has its own stable page so it can be linked from any character, item, location, story post, bargain, curse, or future reward.