There is currently an issue with Deltarune with certain PCs that causes the game to run at the refresh rate of the monitor in Fullscreen, rather than the standard 60fps the game runs at. This causes the game to speed up drastically, and is entirely dependent on monitor refresh rate. For instance, I have a 144hz monitor so this bug makes my game run at almost double speed.

Since Toby is actively working to fix this issue, the mod team has decided to ban the use of this exploit. We apologize for any confusion this may have caused and for it not being addressed sooner.

For the time being, if you are affected by this bug please avoid using fullscreen, as to not provide an unfair advantage. If the game is too small for you, you can download a free program called AutoSizer that can resize small games like Deltarune (and Undertale, by extension) to a bigger window size.

Feel free to ask any questions.