in case anyone's wondering on the sort of creature my sona is within my setting - they're called Spell Devourers and I am actually working on making two stat blocks for them: one that's for my own in-house tabletop system i've been building, and one that'll be for pathfinder 3.5e :)
as for in-setting stuff, spell devourers are pretty rare, almost exclusively the product of magical experiments gone awry (usually ones that are attempting to create artificial life). naturally formed spell devourers are even rarer and tend to not be very intelligent, about on the level of like. a small prey animal. but ones from magical experiments tend towards around the same average intelligence level as other sentient species
yes one of their actions acts like a reflexive counterspell with the bonus of healing [spell level]d4 hit points to them
they can also steal spell slots. and strip enchantments from items. basically throw me at your party if you really really hate the caster one of your players is running