I know this game is dated. I just wanted to do this for fun :)
Links I said I would put down here.
Staying put as instructed -
https://www.youtube.com/watch?v=9YcZhaFHCq4
Creator of Undertale -https://undertale.fandom.com/wiki/Undertale_Developers
Etc. ( Got lazy so you might have to look up the rest.
God Bless!
