I remember reading a story not too long ago when a male human gets a Wonderbolt costume left on his doorstep and after putting it on transforms into a pony Spitfire. I don't THINK it was here but any help finding it would be appreciated.

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I think I saw in on Deviant-Art
https://www.deviantart.com/search/journals?q=Spitfire+tg

edit: Suited Up- Spitfire TF/TG ?

Yep, Suited up. That's the one.

Did a quick search on FimFetch.
Suited Up - FiMFetch.net
The sequel is also on there (Suited Up 2)

Suited up is definitely the story and I didn’t know another author made a sequel to that one so thank you blastdragon I’ll have to check that out tomorrow

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Can you please link me to (Suited Up 2) Electric Boogaloo

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https://fimfetch.net/story/191486/suited-up-ii
Here it is. Had to search for Spitfire rather then the name of the story.

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Never mind, found it.