Board Thread:Questions and Answers/@comment-25347954-20160608225607/@comment-27701762-20160801011137

Pokemon0629 wrote: BeastBoyxRaeRae wrote: You capatalized Fun I have the 1.1 version of Undertale so it doesn't matter if it's capitalized or not... It does, weirdly enough, at least for some things, but in the opposite direction, as capitalizing it undoes the effect.

But there's a random chance each time you enter the hallway that the door will appear. I think it's something like a 10% chance, at least from what I'd been able to find on it. And from what I can tell it was always a random chance of spawning. Unfortunately I can't confirm, since I never messed with the Fun values until after the patch.