She's actually from a Fallout: Equestria story, which only exists in my head atm, where most of my non-NG OC's are from. I'll have to do more of them.
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Pupa is a little baby changeling, she hatched alone or got lost really young, either way she was roughing it for a bit before Fuzzy Dreams and co found her.
She isn't great with her changeling magic yet, so she can only change into a dark filly with wings and a horn. She uses her pony forms forelock and her big pink bow to hide the horn when in towns, which is usually when she uses that form.
She'll get better as she grows and eventually have better control over shape and colour.
Other than being a changeling and all that comes with that Pupa is a pretty normal filly, she loves when they get to spend time in settlements with other colts and fillies she can play with, and often snuggles up to the older ponies, especially Fuzzy, at night.
Her favourite colour is pink. She just loves it. It helped her warm up to Fuzzy in the first place, since she loved her mane.