Find your tribe in a Sea of Creativity
Long post ahead!
So, this is something I haven't really seen anyone discuss or mention hardly anywhere, at all. It's mentioned a singular time, in the Terra Incognita: Adventurer’s Guide to Beast-Yeast, but even there, the only information provided on it is a paragraph of splash text that is more descriptive storytelling than informative research.
It's the Candyceps fungus.
The text accompanying an image of a Candyceps-infected deer reads: “A sleepy silver deer rests its head on the moss… unaware that the Candyceps fungus lies hidden amid it. When the deer wakes at dawn, it will take a completely different appearance… This deer belongs to the Candyceps now. The Candyceps has full control.” (Terra Incognita: Adventurer’s Guide to Beast-Yeast, pp. 20)
(Whether Candyceps came about by evolving from the real-world Cordyceps or by evolving independently of it is entirely up for debate.)
So, not much to go by. The wiki has expanded on the Candyceps fungus a bit, but only in comparison to its likely real-world inspiration, fungi in the Ophiocordyceps genus- most likely Ophiocordyceps unilateralis, to be specific. Colloquially known as just Cordyceps, the real-world fungus is parasitic in nature and is able to take control of a host’s body, the hosts most typically being ants in the case of Ophiocordyceps unilateralis, but some other species in the Ophiocordyceps genus are able to infect other species of insects such as cockroaches, beetles, flies, bees, termites, butterflies, and mantises.
That's… a wide variety of insects. Insects that we see a distinct lack of in the Cookie Run universe, specifically Kingdom. (I'm uneducated on the other games in the franchise, though, so I will really only be referencing the events and content from Kingdom.) In the Cookie Run universe, there are only a handful of appearances from or references to insects as a whole. In fact, there's a distinct lack of arthropods in general. There's a spider here and there, such as the Webbed Spider Queen we see in episode 3 of Beast-Yeast’s world exploration. There's also the beetles we see in The Lost Golden City (which are extremely worrying for other reasons, but that's a different discussion), as well as the mantis we see in the Terra Incognita art book. Both the beetles and mantis, however, have pretty much no information provided for them on the wiki, and very little in the game itself.
Circle back to Candyceps, which, given its real-world inspiration, one could understandably assume would only infect ants or insects in general. But, that's not the case. The one and only infected host we have ever seen is a silver deer, not any of the few insects that are ever mentioned in the Cookie Run universe.
This raises a lot of questions. Why are there so few insects? How has Candyceps infected a deer and not an insect? Is Candyceps able to infect more than just deer?
Let's focus on one thing at a time.
For starters: why are there so few insects? Honestly, I couldn't tell you; I don't know. Where there are so many iterations of all kinds of flora and fauna in the Cookie Run universe, for some reason, there is a distinct lack of insects. Now, one could propose that the Faerie Cookies are insects, but that's not a verifiable statement due to how little we know of the Faerie Cookies, as well as Cookie biology, in general. In the same way centaurs can't be classified as insects just for having six limbs, Faerie Cookies can't be classified as insects just for having insect-like wings. So, Faerie Cookies aren't insects with the information we have available to us currently.
(Tangent)
(That begs the question of what in the world a Cookie can be taxonomically classified as. Given that they are magical beings, possessing sentience and some form of digestive and nervous systems despite lacking internal organs, a taxonomic classification of Cookies may be a moot point because those magical properties are not something anyone could take into account. For simplicity's sake, I'm going to presume that they can at least be classified under the kingdom Fungi, due to Yeast Spores (which appear to serve as a stand-in for eukaryotic cells in the Cookie Run universe, according to the wiki) being “the smallest unit of Cookie life”.)
(This means that everything except for whatever the Cookie Run universe equivalent is of the real-world prokaryotic kingdoms bacteria and archaea contains Yeast Spores. By real-world standards, that means the Yeast Spores are the smallest unit of not only all Cookie life, but also the life of all in-universe animals, fungi, plants, and whatever’s inspired by the species in the kingdom Protista. (Science nerds you are welcome to explain to me what's going on with protists because I literally have no clue about all that.) So, by real-world standards, all in-universe Cookies, animals, fungi, plants, and protists could be classified under a whole new eukaryotic kingdom of their own. (The taxonomy of this hypothetical new kingdom is also a different discussion.))
(For now though, I'm just going to say that since Yeast Spores are yeast, and yeast is taxonomically classified under the kingdom Fungi, everything that contains Yeast Spores is a fungus.)
Anyway, I don't know why there are so few insects in the Cookie Run universe; there's pretty much no information that I've been able to find on that. Next question: how has Candyceps infected a deer and not an insect? There could be a few reasons, all of which can't be verified. It could be because insects were never viable hosts for Candyceps due to them not being abundant enough, or because insects were no longer viable hosts due to them becoming nearly extinct, or some other reason. Regardless of the reason, the Candyceps fungus is observed to have infected a silver deer.
This means it evolved in order to infect a host species other than insects either because the original host species (insects) became endangered, or because deer are just the host species it evolved to infect regardless of the conservation status of insects. If the former is true, it has terrifying implications.
If Candyceps eventually runs out of deer to infect because they become endangered just as the insects had, what would it evolve to infect next? Other fauna of the Faeriewood? Maybe, but what if those species also become scarce eventually? Candyceps is a fungus, and as we've observed in CR:K, a fungus has already successfully infected and taken control of more than just a deer.
Poison Mushroom Cookie; what are they? Were they once a different Cookie who has since been overtaken by a parasitic fungus? Were they originally a fungus that gained sentience? Were they baked like that? Unfortunately, their origin is unknown. In the case of them being a Cookie piloted by a fungus, that shows that a fungus has already managed to evolve to infect Cookies, which means that it's not out of the realm of possibility that Candyceps might evolve to someday do the same. The case of them being a sentient fungus is worrying as well, as it shows that in-universe fungi have the capability to become sentient beings, which, what if Candyceps does the same? Them just being baked like that is fine, but it also seems like a missed opportunity for some insane lore, which is something I don't think the dev team could resist.
In either case, even though Poison Mushroom Cookie and Candyceps are different fungi, the implications of both their existences is cause for concern, and I don't really see anyone talking about it at all. I desperately need to know if anyone has any thoughts on this because if there's ever a canon zombie apocalypse arc I will scream.