Vax developed wings after his deal with The Matron. It was surprising and very recent.

now, you sit outside under an overhang in the cliff face, on a rock outside of the cave where Vox Machina, including you, had just defeated an acid spitting dragon.

Vax was slouched against a sheer rock wall, twisted uncomfortably as he winced and pulled strange faces, trying to clean his acid burnt wound on his wings with the new and strange sensations of them being on his back.