Board Thread:General Discussion v2.0/@comment-27234286-20151118175310/@comment-38451037-20190417024745

The only thing connecting Undertale and Deltarune are the Metanarrative between the two (insert Chara/Gaster theory here).

Other than that, I agree that it could be either a game or the comic in the stretch goal; though I think a spinoff were the most likely scenario.