The main character of Undertale is of unspecified gender, and MatPat was (somewhat clumsily) addressing this by referring to them alternately as "he" or "she", at random. Since the last video, he seems to have responded to criticism by including "they" among the random pronouns. This is pleasantly surprising progress!
@jk not the way I do it (which is probably why I cry so much when playing bideo games)
I meant canonically speaking but that's true too
Generalistic and moderated instance.