In which years later IMP gets hired by the owner of the Sev'ral Timez who is now resign in Hell to kill Mabel,there is a fight between the gang and IMP(Blitzo vs Stan,Wendy vs Loona...) but during that Dipper,Mabel and Wendy get accidentally sent to Hell(so as Robbie when He tries to flirt with Loona to her annoyance when she was in her human disguise as Tambry broke up with him long time ago only to see her transformer and be like "werewolf!" only for Loona with irritation to tell him she is an hellhound).
During their time in hell Mabel become friends with Velvet without anyone's knowledge and Mabel doesn't know Vel is an overlord(in later scenes Valentino comes for them and offer Velvet the honore of torturing them only for Vel having conflicts since she likes Mabel in a hilarious scene like that scene from Emperor's New Groove),Robbie gets chased by demons when they find out he is human only to end up with Angel who makes Robbie sexually confused and Angel sass the hell out of him like "are you sure you aren't Valentino's cousin or something?",Verosika tries to get access to Dipper's holes and even when she learns that he and Wendy are in relationship to their complete bewilderment she offers a "3 way",on Earth Stan and Ford interrogate the captured IMP in which we see a dick measuring contest between Stan and Blitzo to Ford and Moxxie's simultaneous groan and then Stolas knocks the door and ask the most profane question possible that makes even both Blitzo and Stan cringe"oh hello good sire!have you seen a devilishly handsome imp with a *continous BLEEPs* ",Alastor offers a deal to Mabel and Dipper but before he can even finish they simultaneously say "NO!" due to their experience with Bill,Dipper and Mabel and Wendy ends up in Happy Hotel now named Hazbin Hotel.