One challenge in keeping both shows in equilibrium is their conflicting nature. I.M.P are professional killers with little regard for anything outside their own group and personal lives. While Hazebin Hotel has flawed but more empathetic demons involved. Being on opposite sides of goals, there is little doubt the two would not get along. If I.M.P finds out some of their victims have checked into the hotel, or if Angel befriends a now demon Eddie, he'll want justice since he finds violence against children despicable. But obviously Vivian can't have them destroy each other or one defeat the other. No, somehow the two will have to enter good terms with each other and work together if a crossover needs them to. How would you get the two on good terms? Both will require character development.