How to add Gaster in Undertale
To add Gaster in Undertale, you can't really 'add' him. Instead, you can encounter him by changing the game's FUN value in the game's files. You’ll need to edit the 'undertale.ini' file to set the FUN value to specific numbers like 66. Good luck!
Play Games.Earn points.Get gift cards!

Playback Rewards
(13.7k)
500k players and counting...
More Answers
It's like finding a secret boss: to see Gaster, edit the FUN value in the game's files or just get really lucky.
I changed my FUN value to 66, and a mysterious figure appeared. Never been the same since!
Honestly, adding Gaster is totally random and mostly a matter of altering the FUN value in the game. Check out some guides for specifics!
👀 If you like Undertale...
The brands referenced on this page are not sponsors of the rewards or otherwise affiliated with this company. The logos and other identifying marks attached are trademarks of and owned by each represented company and/or its affiliates. Please visit each company's website for additional terms and conditions.
People also want to know
Add an Answer