In the spirit of GoF, meet the world's smallest dinosaur ... type ... thing, the covid-eating 'Microraptor'! He's my entry for the September 2022 Character Design Challenge: 'Hybrids'.

Not to be confused with the prehistoric microraptors, these organisms will take on traits of prey and hosts, such as the flagella of bacteria (tentacles) and the green, plant-like cells of phytoplankton (tail). From covid and tetanus to cancer and parasites, they eat anything that threatens their territory ... namely
your body. Microraptors would be diseases themselves, but they are smart enough to know not to destroy their home. However, without prey, they may turn on a host's gut bacteria, mistaking it for a low-priority invader good for a backup food supply. Once they've eaten all of that, they will start tearing bacteria-like mitochondria from your cells to devour it. Yes, that's ... pretty much as dangerous as it sounds. If you have a microraptor infection, eat plenty of probiotics in the early stages, keeping up the gut bacteria. It is not advised that you live unhygienically just to feed microraptors, although ... that could work, if they are good enough to handle whatever you throw at them. Eventually, microraptors will settle into your body enough to realise gut bacteria is off limits. Domesticated raptors will even develop fondness for their hosts, refusing to eat mitochondria whether they're hungry or not.
Microraptors can survive on the nutrients in a host's bloodstream, but they cannot reproduce without prey. How, you never asked? Their claws are actually embryo-like organelles that grow into new raptors, and yes - the claws have eyes before developing. Once a claw infects a microbe, it grows and bursts out as a young raptor, which is totally not a callback to a certain sci-fi horror movie. Microraptors can either produce brand new packmates, or grow an empty body and transfer their own nuclei to it to live longer. That last part is important for them, since a microraptor's body has a one-to-two-day lifespan. Only the long-lived nucleus survives after that, if it's transferred to a new body in time.
Humans have never noticed microraptors until recently, due to the sheer vastness of the microscopic world. Though they are relatively rare, there are countless packs with different ways of life. Some will tweak your body to peak performance for better chances of survival, though you'll need to eat more. Others will grow fat cells in your body as a backup food source in case they run out of prey, making you gain a little more weight than you'd like and have a hard time losing it. Others live like freeloaders, only hunting when necessary and surviving on the stuff that you eat, forcing you to eat more but without the benefit of extreme fitness. Some will make special efforts to build a relationship with you, using a neuron-based raptors that talk to you through your nervous system. At least one pack has managed to give their human microraptor avatars, allowing them to run with the pack and coordinate defenses. Microraptors almost always have a health benefit, from moderate/mixed to extreme. Some packs will take care of you so diligently that you could live forever. However, if two microraptor packs end up in the same body, they just might go to war and catch you in the crossfire, causing sickness. Of course, there's always the chance they'll get along. However, there are whispers of a hostile pack dubbed 'Flesh Masters', bent on infecting all humanity. Slowly, they make their hosts as monstrously dangerous as a human can be, manipulating them to spread the infection without necessarily knowing. On the flipside, if you form a strong connection with your microraptors, you can ask them to make slow changes to your body. The microraptors can never turn you into Superman, but they can make you an Olympic class athlete, an Einstein level genius or a Tom Cruise-rivalling looker. However, any key change is best made before teenagehood ends, as a fully grown body takes longer to optimise.
Like humans, microraptors are a mixed bag, but do not fear. Most would rather be your friend. After all, a happiness does the body good. Who knows? One day, they may call you 'alpha'!