For
Alastor's Game Backstory:
In this universe, Masha and Vika remain best friends... However, after Vika's father (Bill Cipher, if anything, this is not canon.) was destroyed, she... abruptly disappeared. A week later, Masha managed to find Viktoria randomly, however... This is not Vika, that she knew... In fact, it was none other than... Alastor? It turns out that he needed victims in order to deal with the Pines and avenge his friend (In this universe, Bill and Alastor are also best friends.)... He, in the altered body of Viktoria, with the help of magic sent Masha to a strange place where she needs to escape before the end of the day, otherwise... She will become his victim.... Meanwhile, Vika begins to suspect that this demon (Who pretended to be friendly and peaceful at first...) is not as good as it seems.... It's like... The whole incident is a big "game" for him....
(Role Swap AU - there is exactly the same plot, but now... Alastor captured Masha's body, instead of Vika's body...)