Board Thread:General Discussion/@comment-36624593-20181205013841/@comment-38451037-20190411015547

Toby already told us in the Game's Q&A that while there are some connection between to the two games, their influence with each other was minimal at best.

Hence the Meta is the ONLY thing connecting the two; Gaster themselves have little to no impact on both games narratives but it's implied that he have a hand in the meta, especially with Deltarune. Hell, some could argue that Chara also interfere with the servey just so that they can place OUR SOUL into Kris; and we yet to know if it's the same soul that we control in Undertale (which is my reason why the red trait is YOU). But it's only the same kind of Meta that Undertale been using, yet in Deltarune this has been significally downplayed.