Which wouldn’t make sense if he wasn’t Gaster ESPECIALLY considering that it features many of the Gaster Followers and a character that LITERALLY SPEAKS TO YOU IN WINGDINGS!!!!
Other than the context of Gaster being shattered through time and space, that’s our only piece of evidence from UNDERTALE.. there’s information outside the game that further solidifies that Mystery Man is Mr.WingDing..
With all this evidence even though it’s not 100% #confirmed it’d be real stupid if he wasn’t Gaster (Plus why would Toby say that this is Gaster? He’s never said anything about it and deliberately left it up to us to solve!! IM RIGHT FOREVER AND ALWAYS)