Absolute Villainy

Infamy is a hidden settlement stat that climbs as you do genuinely bad things; the confirmed driver is killing innocent (non-hostile) NPCs. Push it to 100% and this unlocks - which is also the gate that lets you accept the Tyrant Overlord objective for No Rest for the Wicked. Best done deliberately on a "dark" save you don't mind burning. Pairs with Memento Mori.