After unlocking Infusion in Deathloop, one of the best weapons you can find, especially when playing in Multiplayer PvP as Julianna, is the Heritage gun; a combination of a long-range rifle and a close quatres shotgun. To acquire this weapon, head to Carls Bay in the evening, then enter the Fathoms of Lament building, where you will be introduced to a puzzle that will unlock the weapon.