Why are people so sure that Gaster's gonna wind up being a major player in Deltarune when he's never been referenced in Deltarune and had basically zero plot relevance in Undertale beyond being Game Theory fodder? Like, the only actual canon info we have on Gaster is he probably knew Sans, made The Core (which wasn't some god machine it was literally just a thermal power plant), and died when he fell into it. We don't even know for sure what he looked like, the sprite's just called spr_mysteryman and the fandom decided that was gaster