Undertale - No Mercy is the most popular Undertale creepypasta. In the story, a man finds a beta version of Undertale and decides to a Genocide Run. However, the route becomes dark and somewhat gruesome as time goes on. The creepypasta is planned to be revised once the original transcript is redone. The original transcript from DeviantArt was deleted, however, it is currently being retranscribed from a reading by Alex Holden.
I was introduced to Undertale on its release date back in September. My best friend was talking to me over Skype eager and bouncy because the game he had been prepping for for years and years was finally out. Of course, since I didn't like RPGs, I didn't really show any interest and thought it was just the newest fad and it would die out in a few months. My friend eventually gifted me a copy of the game from Steam. Although since he was a really kind guy, but again, I didn't really care. By that time I already knew a few things about the game due to Tumblr and Instagram among other things. I knew there were two skeleton brothers, a sexy robot character and a kind goat figure. Anyways, fast-forwarding to that night...
I was in my bed when the thought of the game came into my mind. Then I finally thought hard enough to give it a try. I mean, it was pretty much free since my friend gifted it to me, and I'm the kind of guy who wouldn't let free things go to waste. That afternoon after work, I parked around the corner and I opened up my Lenovo computer and then opened up Steam. I clicked the game and began to play it... and then I got hooked. I found myself drawing a few pieces of fan-art here and there. I even started a Tumblr ask blog for Sans, and then tried my hand at a fan-game called "Undertale 0: Frisk". I was more of an Undertale geek than my friend at this point. The one thing I really liked about the game, though, was the secrets. Who is W. D. Gaster? Who's the spoon creature that tucks you into bed in the True Lab? Who's the protagonist, and what's their backstory? Those questions went unanswered. Getting to the point, there was a Reddit discussion urging people to dig into the code of the game, mess with "fun" values, look at the secret rooms, et cetera. I decided since I had low Reddit karma, I could find something big and get some upvotes. I could even get some Reddit gold or become well-known in the Undertale community, I thought. I then opened up Undertale and then Firefox. I began to downloade a special software that would enable me to look into the inner code of the game. I then boot up the software and linked it into Undertale. I began to look through the code -- most of it was just piles and piles of gibberish; things I didn't understand. In the midst of it all was some sprites. I found some walking sprites for Chara that weren't in the game, along with a sad Papyrus sprite I had never seen. I decided to download a few more programs to dig even deeper. After downloading them I linked them all into the game. I don't think anyone had dug as deep as I did, because I dug so deep I found things nobody else had found, such as a full set of sad Toriel sprites, a small sprite for the Steam logo and an unidentified woman with broad shoulders, presumably an unused amalgamate.
I called it a day and decided to post my findings on Reddit. But... something urged me to search more. It seemed sort of fun to see things nobody else had never seen, kind of like finding gold in a pirate ship or finding a new type of animal.