Well I'm not going to talk to you about a "creepypasta" about a video game. Believe it or not I'm going to talk you about a real video game, based on My Little Pony, worthy of be considered a real creepypasta.
This game doesn't have great graphics (they are pretty much the NES-style graphics), but it still doesn't diminish its impact.
In the plot, you start off using Apple Bloom. At first, it's not a big deal; Apple Bloom walks, meets Twilight Sparkle, and both ponies walk to the Everfree Forest to see Zecora. When Apple Bloom and Twilight go to her home, something blocks the path. Here is where it starts to get interesting.
Twilight decides to stay and think about how to get around what was blocking the path, while Apple Bloom goes back on the road when you suddenly see a pony going further into the forest and you'll have to follow her. In doing so, you'll get to an unknown town. After you talk with the yellow pony in one of the houses, you'll find a red gem. When you get it, go back to the yellow pony and talk with her. You'll then have to solve a small, but not very difficult, maze and interact with the lever that you'll find.
After doing all that, you'll have to go to a forest part in the north of town. On the right of a house in the forest is a well. Interact with it, and you'll have the key to the house. Use it to enter the house and...well, at that moment, you'll have to see for yourself.
Here is the link of the game. Enjoy it, if you can: My Little Pony - Friendship Is Magic