Rouxls is a bootleg version of Gaster

>Gaster speaks eloquently – Rouxls speaks in a way that’s supposed to imitate a smart and cultured person
>Gaster is very mysterious, and people have been trying to “solve” him for years – Rouxls constantly creates shitty puzzles for us to solve
>Gaster has control over the game itself – so does Rouxls, he just really sucks at using this power
>Gaster was the second in command for Asgore (and in meta sense for Toby) – Rouxls constantly tries to find some bad guy to serve as the main henchmen

It will be revealed that Rouxls is a fragment of Gaster or something that becomes alive in the dark world, but since he’s only a part of him, he can only poorly imitate the whole person.