UPDATE 31/10/2018: Since the events of earlier today, in which the Undertale Twitter account released an entirely new game onto the internet with no warning, multiple players have reported issues when uninstalling the game.
According to those who have (somehow) already tried to uninstall the files for Deltarune, the uninstaller deleted anything else that was tucked in the same folder as the game files. So if you kept the game's uninstaller contained in a separate game folder (the recommended installation process), you should be fine: but if you popped it elsewhere, you might lose that entire folder - along with all the files it contained. Yikes.
As a heads-up, #DELTARUNE will delete the entire folder it's installed in when you uninstall it. Make sure SURVEY_PROGRAM is its own isolated folder with nothing else in it but the necessary files!— Dan Parker (@FretLegend) October 31, 2018
Undertale creator Toby Fox has since tweeted about the situation, explaining the uninstaller "deletes the entire directory" where it is placed. To combat this, he suggests entirely avoiding the game's uninstaller.
Hey apparently the uninstaller for DELTARUNE just deletes the entire directory the uninstaller is in. Depending on where you installed it, this could have some consequences. I recommend you don't use the uninstaller.— tobyfox (@tobyfox) October 31, 2018
Of course, many have since made light of the situation - particularly given users are greeted with the words "you will accept everything that will happen from now on" when installing the program.
Re: last RT— Mask the audio guy (@zMASKm) October 31, 2018
You can never uninstall Deltarune.
It's stuck with you forever.
You cannot escape.
ATTENTION ALL UNDERTALE GAMERS— Conchobhar ? (@AssassinWolfRE) October 31, 2018
Deltarune may delete everything in its file if you uninstall it so tuck it away behind something else.
TO STOP THIS ALL TOBY FOX NEEDS IS YOUR CREDIT CARD NUMBER, 3 DIGITS ON THE BACK AND THE EXPIRATION MONTH AND YEAR
Meanwhile, it increasingly looks like Deltarune is an entire game in itself, rather than a teaser as previously thought. If you haven't tried it yet, you can find the files here - just make sure to watch where you install them.
ORIGINAL STORY 31/10/18: After yesterday hinting some sort of announcement was on its way, Undertale's Twitter account has today shared a strange link - one which leads to a very mysterious website.
Following the link leads users to a site called "deltarune," which as some fans have highlighted is an anagram of Undertale. The site then asks users to "read the final warnings" and "refrain from discussion of the program for 24 hours". Whether anyone will listen to this is pretty doubtful, but it is pretty dramatic.
After clicking the download link, players are asked to "accept everything that will happen from now on" before installing the files, initially called a "survey program". Very ominous, and very Undertale. The familiarity doesn't stop there, as the files lead to a character creator and game of some description. Without giving anything away, the game whisks you to the surface of Undertale's world in a setting that seemingly takes place after the events of the original game. Or perhaps it even takes place before? It's still not clear.
Many are speculating this could be the preview for an Undertale sequel (or prequel). Yet with players still working their way through the teaser, we're still not entirely sure what it means, or how long it will last - although I am filled with determination to find out. Stay tuned for more.