MCF: System Shock, Quaking Palm

Your System Shock feature improves with your mastery. You learn some of the most lethal fighting moves known by only a select few individuals.

The most common of these is the ability to set up lethal vibrations in another's body, called the “Quaking Palm”.

When you hit a creature with an unarmed attack, you can spend 3 Focus Points to instill imperceptible vibrations, which last for a number of days equal to your Class Level . The vibrations are harmless unless you use an action to end them, while you and the target must be on the same plane of existence.

When you do, the creature must make a Fortitude Save.

If they fail, they take Shadow damage equal to 10d10 + your proficiency bonus + your character level. If they Critically Fail, their hit points are reduced to 0 and instantly killing them with the Dead condition, as you take their life. They cannot be resurrected by abilities that revive creatures before 10 days.

You can have only one creature under the effect of this feature at a time. You can choose to end the vibrations harmlessly without using an action.

Your subclass may give you another version.