Assassin is most thematically on the nose for Dark Urge. Warlock doesn’t synergize great with rogue aside giving you a bit of utility magic, which is nice.
If you want to multiclass as an assassin, gloomstalker is the smartest choice.
If you want to be a monk, you’re better off picking thief over Assassin for your rogue subclass.
gloom stalker assasin is the most boring multiclass combination that ever exist in game. It's not the Skyrim where every build go to sneak archer
