#human!gaster

Also, 5 years of progress in comparison with the old family portrait :>

Okay, theory time, Gaster was a human. Nowhere in the game does it describe Gaster as "monster," only "man." It said that Gaster split across time and space, and the thing is, monsters souls only dust, but a HUMANS SOUL splits, and it said that he scattered across time and space. Maybe some parts of himself remained in Undertale, but some parts of him were scattered into Deltarune. A thing that I theorized he opened a portal to using the machine Sans has in his basement and that machine in the old labs. But anyway, Gaster was a human, Sans and Papyrus were originally from Deltarune, and the entirety of the underground is the dark world. But I dunno.