A dragon is terrorizing a city/town. Some pony (your choice) decides to take matters into their own hands, and swallows the dragon during its sleep. Includes post-vore growth and/or weight gain.

Silverstar took a step closer to the dragon, and flinched back when it rumbled. Its every exhale brought another wave of smoke to flood the cavern floor, warming his hooves.

It rumbled again - snoring, Silverstar realized - and fidgeted a bit. Silverstar grinned. Good. That meant it was still asleep. It was time to get to work.

He started with the tail. It was long and thin at the tip, just like a noodle. He was able to get his jaws around it easily enough. From there, it was just a matter of slurping it down, his jaws slowly widening around it until he hit base. Until then, he just enjoyed the feeling of his belly slowly filling, growing underneath his hoof until it bulged out obscenely over his knees. Fifteen feet of dragon tail didn’t look like too much in any one gulp, but over time, it all added up.

Silverstar took a second to catch his breath. He shifted his weight a little bit and tried to steady himself on his haunches. His big belly was making that a bit more difficult, though, as it weighed him down and pulled his center of mass forward. It took only a few more moments for him to find a comfortable position, roll around his jaw, and then - with the tail still stretching his jaws wide - open even wider.

It was amazing, really, that the dragon didn’t even stir as Silverstar’s mouth opened wide enough to take in its fat, muscular haunches in their entirely. Even lying down, the dragon was twice as tall as a pony, but Silverstar managed to fit his mouth over the whole thing. An onlooker would’ve probably called it an insane or even grotesque sight, but the stallion himself was too focused on his herculean task to care. Slowly, pacing himself, he gulped once - and a little bit of the dragon’s rear slipped into his maw.

Then again. And again. Soon enough, the entirety of the dragon’s hindquarters had joined the tail in his jiggling, sloshing belly - by now bulging far larger than the rest of his body - but but Silverstar wasn’t done yet. He kept going, taking in the back legs, and then the stomach. His neck bulged out incredible as the dragon’s entire back body filled it, soon followed by his stomach. Feeling a sudden surge of energy, Silverstar just tossed his head back and lifted the rest of the dragon into the air.

Amazingly enough, it worked. The rest of the dragon up to its shoulders just slid into Silverstar’s belly with an earthshaking plop, the force of gravity doing most of the pony’s work for him. He took a second to flex his now shrunken jaw around the neck of the dragon, loving the feeling of his gurgling, twenty-foot belly going to work on the enormous body inside of it.

And then, finally, the dragon awoke. Its eyes opened wide, and its jaw was quick to follow, thrashing from side to side and spraying smoke in every direction. But Silverstar’s jaw was quicker. Quick as a wink. he opened as wide as he ever had before, and gulped the rest of the dragon down - and swallowed.

He let out a huge sigh of relief. It was done - his town would be safe once more. One hoof patted his enormous, dragon-sized belly. It was a gurgling, happy belly, and a happy belly made for a happy Silverstar. Once, every so often, the dragon would lurch around inside, or else exhale another flood of smoke - which Silverstar would release in a dragon-sized burp - but soon, the thrashing stopped, and his belly settled down to the happy work of digestion.

As Silverstar slept off his meal, more than completely immobile by now, something odd happened. Just as the dragon was added to Silverstar’s figure, so was its magic. He snored loudly as size crept up his body, growing not only horizontally, but vertically as well.

When Silverstar finally awoke, he found the tip of his head scraping the ceiling of the cave. “What the - “ he grunted - and then stopped. There was his backpack, holding all of the survival tools he’d used to get here, lying on the ground. Slowly, he reached down and picked it up - with a single hoof. It sat there, tiny and incredibly light, for all of the effort he’d struggled through in carrying it the day before.

As realization set in, Silverstar grinned. “Well,” he said, getting to his hooves. His plush, oversized belly swung between his legs, its gurgling suddenly getting a bit louder. “Looks like there might be a new dragon in town.”

Or, at the very least, a very dragonish pony.