Undertale's creator Toby Fox has taken to twitter to tease something related to the game that will be revealed tomorrow on the official Undertale twitter account.
For those who completed UNDERTALE it's really important that you check @UNDERTALE 24 hours from now.
I want to make something new, and it all begins with your feedback.
A Windows PC / MacOSX PC is needed. https://t.co/N1IJLyiswy
— tobyfox (@tobyfox) October 30, 2018
The obvious guess, of course, is that the surprise is Halloween related as tomorrow will be the 31st of October. However, Fox also states that he wants to make something new based on fan feedback for a Windows or Mac PC. Which could mean its an expansion to Undertale or a sequel, which would also make sense of the timing. For a game about a bunch of monsters trapped under a mountain, Halloween is the time to make any new game or DLC announcements.
IGN did some digging on the Undertale twitter account and found this:
The official Undertale Twitter account has blacked out its thumbnail and visible username, tweeting out a series of all-caps messages suggesting something will be announced tomorrow. For reference, the characters Papyrus and Mettaton are both known to speak this way, though Mettaton stops doing this once he transforms into Mettaton EX.
The full message spread throughout the tweets reads: "WELCOME. HAVE YOU BEEN LOOKING FOR ME? HOW WONDERFUL. I HAVE BEEN LOOKING FOR YOU AS WELL. I HAVE SOMETHING, SOMETHING I WANT TO SHOW YOU. SOMETHING I THINK YOU WILL FIND VERY, VERY INTERESTING. BUT IT IS NOT YET COMPLETE. NO, IT IS FAR FROM COMPLETE. THUS I HAVE A SMALL FAVOR TO ASK OF YOU. RETURN HERE IN  HOURS. AT THAT TIME, I WILL ASK YOU A FEW QUESTIONS. THEN, USING YOUR RESPONSES, WE WILL APPROACH ITS REALIZATION. THANK YOU VERY MUCH FOR YOUR TIME. I WILL BE IN CONTACT AGAIN SOON.
It appears as if we'll have to wait until tomorrow to find out what exactly Fox is planning, but it's sure to be a treat.