The Monsters Mythos – You gain a new stat called Rage, which has a maximum value of hard+weird, so long as weird is above 0. When you cause brutal, callous and unmitigated devastation, such as ripping an enemy totally to shreds, increase your Rage by one. You can spend a Rage point to turn a missed Act Under Fire, Go Aggro, Raw Combat and Teramach move into a partial hit, but it’s not going to be pretty for anyone involved, including you. While you have at least one Rage point, you are incapable of showing any restraint in your attacks, you cannot flee from battle, and you can never, never show mercy to fallen enemies. Any creature that attacks you in any way is treated as an enemy for all purposes.
Balance? Broken? Basically, whenever the Teramach (name of playbook) misses a roll, they can decide, no, no I don't think I did miss that roll, and their callous disregard for morality, common sense and physics makes it so. Hard moves all round, of course, for whoever is standing next to them.
Thoughts? I'm tossing up what the max should be, I've used hard+1/2 level, hard+weird, hard±weird, each of which has pros and cons. This is the core move of the class, and several others manipulate Rage in a variety of ways.