After the Dark Souls Age of Fire mod, the Datahacks team released Forces of Annihilation – a similar hobby project for Dark Souls 3. As of now, FoA lets you storm Lothric as the game’s enemies and bosses alike.
I especially like it when a yhorm the giant wanders through the desecrated capital and hits headless gargoyles. Head to the 5.40 mark above to see this in action.
With installation and use in mind, Datahacks has a tutorial series of three videos all about attaching the mod to the game and owning bosses and enemies. Toggle camera and attacks yhorm the giant and phase changes; and regular and improved enemy controls.