Resolves YES if, through Deltarune or other undeniably canonical means, the mystery man sprite in Undertale (pictured below) is confirmed to be W.D. Gaster. Either because in Deltarune, Gaster or one of Gasters' appearances strongly resembles this sprite, or there is other dialogue or something to that effect strongly suggesting this was Gaster. (in a way that the other goners aren't - it wouldn't count if they were all "equally" Gaster)

Resolves NO if, after Deltarune has completed, (and waiting a couple months for anything to be found in the files/some ARG that releases soon post-Deltarune or whatever), there is no strong evidence that the mystery man was W.D. Gaster.

This market may require some discretion, so bet with caution. I may bet in this market but I will be happy to defer to public opinion in resolution if me being biased is a concern.