We can't. Copyright issues. Unless you meant a game SIMILAR to undertale in which case it would probably take up too much data to publish, but someone might be able to do it. But don't get this just for one game. Look at SmileBASICsource, it has alot of cool programs on it.
Fan games from both FNaF and Undertale are both legal, their creators said so.
(I feel horrible having to use both FNaF and Undertale in the same sentence…)
