In the crossover you mentioned that but is that also a thing in the main au?
Part of a small hc I have for cookies is that, at a young age when learning magic they'd usually pick one magic type and stick to it, which let's their dough become accustomed to it. Yes you can learn multiple elemental types although that's much more difficult.
And it works perfectly fine with cookies who STICK to that magic type. That's the intended use, if you use magic outside of your usual you run the risk of getting poisoned from it.
Blossom USED to major in light moon magic. Still Pure Vanilla Cookie at the end of the day.
Unfortunately, though, it bites him back consistently now that he's switched to dark moon magic for the exact issue I mentioned earlier; magic poisoning.
Blossom's main problem nowadays is not overdoing it with using magic in general. It's very hard for him to hit his limit, and so many cookies (both crossover and otherwise. Believe me this has happened before) have assumed he struggles with overexertion (loss of energy via magic) instead of poisoning (overabundance of the wrong magic in body).
Magic poisoning functions on a very simple regulation issue; internally for a cookie, their dough is able to process their magic naturally to prevent it hurting themselves, and recede back to safe levels after consistently using high energy spells for some times. When using the wrong magic type, however, it's like placing the wrong magical substance inside the dough and hoping it processes the same way. It won't. Instead it'll clog up the system and start risking an overflow if the user uses that magic too much.
The only way to fix this is by either draining the excess magic or using your actual magic type you were grown into to forcibly recede the levels.
Now, Blossom can do the former, but never the latter. Why? Because using one type of magic for so long past the safe transition period will now actively hurt him, instead of y'know, helping him RECEDE THE OTHER MAGIC. So he's stuck in this consistent loop of regulating his magic to prevent an overflow while being unable to fix it naturally.
Magic poisoning manifests a lot like a very, very horrible fever. It can oftentimes make cookies get very shivery with a high fever, lethargic, etc. Body overheats so much internally the outside starts feeling too cold to compensate. General war on the senses until it calms down (which can take a couple days depending on the severity)
Blossom has recounted at least... 125 times over the years since he's been hit with the effect. Which may seem like a lot but remember this is spanned over a 3.5k to 10k year time frame. Pretty long length makes the amount of incidents spread out a lot.
Still not a good thing, though. Blossom is usually good at regulating his magical output and will usually prepare in advance after using a high energy spell to cool off with not using magic for a while. This strategy does fail whenever he gets interested in using new spells or experimenting with things he doesn't understand yet.
Tl;Dr using the correct magic type too much causes overexertion, using the wrong magic type too much causes poisoning. Magic poisoning manifests as a severe fever normally.
That's the general gist of it.
