Maybe it should be set in the caves below canterlot.

What's more scarry and 2spooky than colorful tiny horses?.... SCP-COLORFUL TINY TINY HORSES.
It must be done.

Is this a full conversion mod where the main gameplay mechanics are changed or is this something like the SCP Slender Mod?

Several random ideas, cause I am that kind of person.

Location: Now this idea has been thrown around a bit but I want to put my own ideas down. Now you can go for either two options. A location that exists withing the MLP universe that makes sense for a scenario like this, or you make an excuse for why there are "ponies" and other interesting creatures in this kind of facility.

To this end you could make up the story that this is some kind of Human research facility that is cataloging and maybe experimenting on MLP creatures, this would give a good excuse to have SCP-173/106 like creatures attacking the player, or why their are MTF's/Soldiers chasing the player.

Player: Again you could either go for a Human who is trapped, or a pony that has been trapped. Either way, but size may be a bit of a concern if you go for a pony, though you could make the pony move faster, or not blink as much.

Inventories: Assuming the player is a pony you may want to heavily limit their inventories to only a few spaces, at least until you get some pockets/backpacks.

Take what you will.

Any progress?

I made a logo, not sure if it's going in though.

Best progress ever

PD: I have conquered the forums

Nope

Yeah i have proof

Is that a Pewdiepie video I see? :3