The luna game series consists of multiple, very short (4-10 minutes each), and badly made games made in game maker that feature jump scares (mostly featuring pinkie pie) and absolutely dreadful environments. There are a total of 6 games (luna game 0 demo, luna game 0, luna game, luna game 2, luna game 3, luna game 4.)
http://www.lunagame.net/ (click the projects tab to watch a creepy video that very well acts as a "summary" of the tone of the games)
NOTE* you may have to wait about 8 seconds before the video displays anything other than a black screen
For luna game 5 (a fan game of a fan game) visit this link
http://www.equestriagaming.com/2012/02/luna-game-5-creepypasta.htmlThe game "the story of the blanks" is a relevant suggestion as well.
http://www.newgrounds.com/portal/view/573755The game "super filly adventure is also relevant, and is perhaps the most deserving of your attention here, but getting to the creepy part requires some effort.
http://www.newgrounds.com/portal/view/5791655 Tips for getting the creepy ending. (I may have forgotten something)
1. Talk to everyone (including the animals/pets) until they run out of unique dialog (dialog repeats).
2. Make sure you talk to pinkie pie
BEFORE you deliver all the messages (and
DON'T TALK TO HER after you deliver all the invitations).
3. make sure you exhaust zecora's unique dialog
before you make the muffins (to stay on the safe side of things).
4. Bake the "
good muffins" (the ones that you produce when you obey applejack's instructions) and then give them to derpy, then exhaust derpy's unique dialog.
5.
MOST IMPORTANTLY set your computer's internal clock to 11pm-6am (but just set it to 2am to be safe)
before you play so that the creepypasta ending is enabled.
If you followed all the above tips, go back to zecora and if her eyes are black, bloody, and creepy, you have done everything right (you should know what to do from there).
There is also a demo of a game called "silent ponyville" that is a spin on silent hill (kinda obvious) and despite that it didn't creep me out, it tries to be creepy and thus, I will post it here.
http://silentponyville.blogspot.com/ (just search for the link to the demo).
Here is a non-creepypasta luna game titled "innocent luna game"
http://biancagames.com/Luna_is_Cute1.zip that pays a homage to the original creepypasta, and may be worth a playthrough.