"There is an easy solution we are overlooking," Gunn says. "I am no expert on fiendish physiology, but I imagine separating the head from the torso would be effective in eliminating the threat this creature poses. Not just to ourselves, but to all good people and creatures in the universe. Surely we can agree that an archdevil is beyond redemption?"

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Gunn can spam Dominate (DC 30) indefinitely as a class feature. And then would have a Pit Fiend at his disposal. Just think of all the GOOD he could do!