Basically if you go into the files and look closely at Ralsei’s third running animation frame, you can see some text that says “I am the friend inside”. In Undertale, if you kill So Sorry and then get judged by Sans, he will say “i remember you’re friend inside me.” This means that Ralsei is Sans, Sans turns into Ralsei by going into the dark world because he ate Asriel.

This ties nicely with the fact that Henry Stickmin created Deltarune with Gaster because he was so tired of having to make choices that he made a game where your choices don’t matter. He called Charles to crash his helicopter into Hometown, creating a dark world that the shelter was built around.

Of course, we all know that Flynn Skylanders will show up in Chapter 5.2, who is a pilot just like Charles, and he matches the Toys To Life theme of Deltarune. From the hints that Toby Radiation Fox has given, we can infer that Flynn will kill Asgore and Ramb will use Asgore’s soul to wingding the universe while Goku stands there and watches.

In Undertale 2, there’s a hidden scene where Garfield eats a lasagna, then he farts and dies. This matches what the last prophecy says.

Of course, Ramb won’t get far in his plans, because Jockington (the Knight) will punch Ramb in the face, then Susie will punch Jockington, and she will announce herself as the true villain. Kris and John Mantle will have to team up with Spamton and Waluigi to defeat Susie Stickmin.