Princess Celestia's Living Toilet (Scat)

When you wake up, you are tied up and gagged with a pair of Celestia's gross underwear. Luna's shit has been dissolved by your saliva, and it fills the surface of your entire mouth with it's brown, filthy essence. The combined taste of Celestia's backside and Luna's shit, is probably as disgusting as drinking diarrhea directly out of a dark mares asshole. You should know. But the limited amount of it, makes it somewhat bearable.

You hear hoofsteps approaching. More torture awaits you. Two giggling horse-goddesses appear on each side of you. You don't even struggle, you just try to mentally prepare yourself for what you can only imagine is going to be extremely stinky. You weren't wrong.

They lay their divine asses down in front of your face, moving their tails out of the way so that their anuses are exposed. You wrinkle your nose, mostly due to the everpresent stench of Celestia's butthole, being smellable at quite a distance. Looking at their posteriors right next to each other, you determine that your owner's backside is about 25% larger than her sister's. Luna's anus seems to be slightly bigger though.

You see the blanket levitate and land over your face, trapping you and the two dirty, pony-asses in an air-tight chamber together.

Farts... You know what is coming. It makes you gulp, and then gag as luna's disgusting shit, (that sill fills your mouth,) slides down your throat.

You feel your body being dragged closer to their large backsides, the ass-stench increasing as your nose gets closer to their assholes.

One dreadful moment later, you find each of your two nostrils pressed tightly against each anus of the pony princesses. You have two buttholes pressed against your snout, and you're left with no choice but to smell both of them directly.

Celestia's unkept rectum is naturally the stinkiest, but combining it with the still quite pungent smell of Luna's, somehow makes the experience worse, possible because having an anus pressed against each nostril makes for the most potent ass sniffing possible. It doesn't leave that tiny air pocket regular ass-sniffing tends to do, so every breath you take, is the purest butt-smell you've sniffed up yet.

You find yourself almost wishing they would just get to the farting already, just to change the stench up for a while. Emphasis on almost.

Suddenly, they both start giggling.

They both push their anuses harder against your nose, preventing you from breathing. You get ready for the farts.

When Celestia's anus finally expands, and the stinky ass-air leaks out of her, you find out exactly what this position means for fart sniffing.

Her anus and your nostril is locked together as tightly as it possibly could be, and so her entire fart leaks directly into your lungs with not a single molecule of it going to waste. You may be unable to breathe air due to the two assholes, but those same two assholes sure can give you something else to breathe.

Celstia's gas reeks to the heavens of rotten eggs. It smells unhealthy, and it stinks way more than any ordinary fart should, probably didn't help that it wasn't being filtered in the slightest. What you were smelling, was a fart in it's purest form.

Soon after Luna's butthole joins in, with a potent but classic cloud of gas. Its smell was tangy, strong and slightly like boiled broccoli. It wasn't quite as overwhelming as her sister's, but it was still really, really stinky.

Together, they fill your lungs with their anus-air.

As your body fills to the point that there is no more room for their gas inside of you, they relax their rumps and let you exhale. You can still smell it on the way out. As soon as you finish emptying yourself of farts, they push their butts back into your face, and farts again.

This continues for a while. No oxygen, only methane gas. Celestia is clearly using magic to keep you conscious, because going this long without air, would have made anypony pass out long ago. Maybe even died...

You are fearing for your life. Your heart-beat has already started to slow. The Princess' are having too much fun torturing you to notice you are dying on them. But in your fear, you find relief. If you die now, it'll all be over. You will never be mistreated like this again. You relax. Relax the best you can while being filled over and over by the stinkiest farts imaginable. Moments later, your hopes are shattered, when the princesses move their asses away from you, and the blanket is lifted. Celestia, erases the spell keeping you conscious, and you immediately pass out, you're barely alive, but alive nonetheless.