Image imported from derpibooru 
Original Description:
 
It had been a hard and very weird day, but Scoots was feeling really good about herself. Sure, she was still sore and everything was weird, but it didn’t matter - and the mound of pillows and the Pegasure undies Dash had gotten her went a long way helping with any discomfort.
 
What was important was what she was holding: what she had made, and how it proved that despite her limitations, she was very much a real pegasus.
 
More story here (warning: super EXPLICIT, oviposition, weird!)  
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Not really sure how to tag this, but guess I’ll go with questionable (also probably weird enough to be not_texmex, despite this being the only version). Also, she’s not wearing diapers, they’re special underwear pegasus mares wear after they lay their eggs (anatomically designed to provide support and contain any residual leakage).
 
TL;DR pegasus mares lay eggs like chickens do.
 
It’s not exactly a Christmas pic, but it’s certainly a hard package! Merry Christmas everypony.