How to Acquire
Corvo Attano or Emily Kaldwin must kill Paolo three times during their campaign. He will first appear during the mission The Clockwork Mansion when visiting the black market shop in the Aventa Quarter. Talking with the shopkeeper for the first time will trigger his arrival along with two Howlers, and he will stay in a nearby alley afterwards. Killing him will make him disappear and summon rats who will attack the protagonist. This will also give a Special Action for the mission's score.
Paolo will appear again in the Dust District during the mission of the same name. Once dead, he will reappear upstairs in the Crone's Hand Saloon. Eliminating him a third time will complete the achievement. Note that dispatching him the first and second time will not count as a kill for the missions' score.