Undertale and Deltarune creator Toby Fox highlights “rivalry” between Sans and Mob Psycho’s Reigen again

Roughly 24 hours after wishing everyone a Happy New Year with a tongue-in-cheek cartoon of Undertale’s Annoying Dog (which also serves as his online avatar), Undertale and Deltarune creator Toby Fox realized that his first post of 2025 was rapidly getting more likes than any of his other cartoon posts. Specifically, his drawing of Undertale’s Sans and Mob Psycho 100’s Reigen Arataka has now been dethroned as his most-liked post on X (formerly Twitter). 

As a fan of memes and culture, Toby Fox occasionally makes content that references incidents the occurred on other Internet platforms. Last year, Fox posted a full-bodied Sans standing beside Reigen making the peace sign as they greet the reader with “Happy Valentine’s Day.” This post referenced the infamous Tumblr Sexyman battle between Sans and Reigen from 2022, with Sans ultimately gaining the title by 0.1% of the votes. This led to a whole host of fanart either shipping the two characters or portraying them as rivals (affectionately known as SansGen). There was even a joke that the intensity of the poll caused the death of Queen Elizabeth II. 

While Undertale is a video game that follows the story of a child who finds themselves in the Underground realm filled with strange monsters, Mob Psycho 100 is a manga turned anime and television drama that centers on the young Shigeo Kageyama (Mob) as he struggles with school life and controlling his psychic powers. To help keep Mob in check, con-man Reigen takes the boy under his wing under the guise of being a spirit medium. Created by the Japanese manga artist known only as One (best known as the creator of One Punch Man), Mob Psycho 100 tells a surprisingly heartfelt tale amidst its humor and supernatural elements.  

The Snake Year post currently has 294,000 likes on X, which is slightly more than the Reigen post’s 263,000 likes. Now the New Year post is top dog, Toby Fox used the opportunity to draw attention to the fan-favorite shipping pair that it was replacing.  

UPDATED 01/06: This article was updated to reflect the rivalry/shipping history between Undertale’s Sans and Mob Psycho 100’s Reigen.