Even Temmie, a species of monster named and designed after the main artist of the game, appears in the school in Deltarune. Ralsei clearly looked like the young version of Asriel that players meet at the end of a True Pacifist run in Undertale. While much of Deltarune features a brand-new cast of original characters such as Susie, Queen, and Lancer, other faces are more familiar. Additionally, Deltaruneis an anagram of the word 'Undertale,' leading many to believe it's some sort of alternate universe. But it's difficult to blame players for speculating when many of the characters overlap.
Toby Fox is glad to see fans finally treating the game less likely a sequel or prequel and more like its own entity. Though two chapters of Deltarune have been released with the latter coming unexpectedly recently, it's still unclear exactly how it relates to Undertale.
