Undertale Yellow (stylized in all caps as UNDERTALE YELLOW ) is a turn-based role-playing game based on Toby Fox 's Undertale , serving as a prequel. The project is led by Master Sword and is developed on GameMaker: Studio .
It is notable for having famous faces behind the game's soundtrack, such as NoteBlock , MyNewSoundtrack , and Master Sword. Its first demo was released on November 30, 2016, and the complete game released on December 9, 2023. [ 1 ]
Undertale Yellow 's battle system reuses many of Undertale 's mechanics, with turn-based bullet hell rounds and a system allowing Clover to fight or spare their enemies. However, the game deviates from Undertale in a few aspects.
One notable deviation from Undertale is the fight mechanics used. Instead of Undertale 's stretched oval attack board, Undertale Yellow uses a circular target attack board to represent the aim on the Toy Gun . A ring starts from the outside of the target and quickly closes inward. The closer the circle is to the middle when stopped, the more powerful the attack will be. If the circle gets to the very center without being stopped, the attack misses. Another deviation from Undertale is that ammo equipped does not change the method of attack. Instead, partway through the game, Clover obtains the Wild Revolver , permanently changing the battle interface to use six rotating targets instead of one stationary target. The other actions Clover can take on their turn are the same. The dodging system is the same as the original Undertale ; the gimmick of changing the SOUL's color to change the protagonist's movements is not present in Undertale , but various boss battles affect the interface and the way Clover's SOUL can move in a similar way.
As in Undertale , the game can be beaten without killing a single monster. Undertale Yellow retains the witty writing and character focus of the original Undertale . It keeps the system of three main routes, with Clover being able to embark on the Neutral , Pacifist and Genocide Routes .
The Underground has been expanded, with the player being able to explore previously unseen areas throughout the game. As in the original Undertale , puzzles have to be solved in the overworld to progress, many of which are deactivated on a Genocide Route. The final game includes a run button.
As explained in Undertale , many years ago, war broke out between humans and monsters. Humans won and sealed monsters inside the Underground with a magic barrier that could only be broken with seven human SOULs. Undertale Yellow follows the journey of the seventh human that falls into the Underground, and the sixth SOUL to be collected by Asgore . This human is a child named Clover .
Undertale Yellow begins an ambiguous amount of years after the war, after five human SOULs have been captured and not long after the experiments that led to the creation of the Amalgamates . Clover heads up the mountain to investigate the disappearance of the five humans. They deliberately jump into the Underground. There, they quickly end up off the path seen in Undertale and team up with Flowey , who tells them the previous humans had been killed by Asgore. Flowey SAVEs for Clover as they explore new locations in the Underground and decide who to kill or spare in pursuit of justice for the previous humans.
Undertale Yellow started development on February 4, 2016. Master Sword thought of the game and several ideas for it one night, and the next day hurried to find enough people to make it a reality. [ 2 ] Before the game's development began, Master Sword emailed Toby Fox to ask if they had permission to create the game. He responded with simply "Do what thou wilt." [ 3 ] Its official Twitter account has been used frequently since February 18 to reveal new information about the game. On March 28, the game got a Game Jolt page . It gained more attention on April 30 when the official trailer for the game was released. Months later, on November 30, the first demo for the game was finally released to the public.
The game got several progress reports in the years after the demo's release, as well as teasers for different areas of the game. Very early in development, the idea of all battles using the Mettaton shooting mechanic was considered, but soon discarded. [ 4 ] Before the final game released, Master Sword stated no young versions of the main characters from Undertale would appear. [ citation needed ] He also confirmed that W. D. Gaster , Sans , Papyrus , and Undyne would not appear in the game. [ 5 ]
On January 17, 2022, the development team announced they planned to release the game during the beginning of 2023. [ 6 ] [ 7 ] However, on March 5, 2023, the team announced that they were delaying the release to later in the year as their ambition ballooned a lot, requiring a lot more work that would put strain on development if they tried to rush through it. [ 8 ] On September 27, the game was officially feature complete. [ 9 ] Two months later, the final release date for the full game was announced as December 9, 2023. [ 1 ] An official Undertale Yellow Tumblr account was made on November 23, 2023 which answered some questions about the game shortly before and after its release.
On December 14, 2023, version 1.1 was released to fix some common issues players encountered.
On July 13, 2025, version 1.2 was released with some small fixes. The changes were correcting typos, adding a Genocide Route blocker to the Steamworks , changing some credits, and attempting to patch a glitch at the end of the Ceroba battle.
On July 30, 2026, version 1.3 was released. It features various gameplay tweaks and new sprites for the characters that Ryla drew.
Developers have mentioned a possibility of making further versions in the future. The developers have confirmed that Martlet 's house would be added in this potential update. [ 10 ]