Image imported from derpibooru
Original Description:

After some time of huffing, and getting the pegasus quite a bit larger, the earth pony was growing somewhat tired. Surely he was more awake by now, she thought, and as she leaned herself back to the area between his now-rounded belly and overinflated flanks, her eyes fell to the inflatable bellows on the floor. She leaned over to pick them up, resting them on his belly for but a moment, some squeaks being heard as he stirred beneath her. “Right, think I’ve given you enough huffs of my own by now…”

“Nnh, huh? Whahappened? Where…” The pegasus blunk as he came to his senses again, the cool vinyl of the bellows on his belly and the firm squish of the earth pony at his waist being the most prominent sensations. His vision soon focused in on the blue vinyl of the nozzle, looking just past it on the right side to see the small tank attached; it took him a moment to recognize, but as the grey hoof of the earth pony opened the valve and leaned forwards, his eyes bolted open. “T-tavi, wai-mmph!”

“There we go, this’ll get you to shape much faster, I imagine. And hopefully have you wake up, finally…” The grey earth pony loosed a small chuckle as her belly pressed into that of the pegasus underneath her, hooves reaching to secure the bellows in his muzzle before moving to the handles and spreading the sides of the implement of inflation apart. The panicked cries of the pegasus were drowned out by the hiss and squeaks of vinyl, his clumsy overinflated hooves unable to help him as he watched, all too aware of what the earth pony had unknowingly set in motion…

Hopefully she’d have the sense to figure it out soon enough - and not get herself stuck before she could halt it.

My entry for Winterlight’s contest, a little self-indulgent sequence. Shenanigans ahoy~