!CONTENT WARNINGS! The following contains mentions of sapient species eating other sapient species, and also mentions of reproduction (or, rather, the lack thereof). Proceed with caution.
Monsters
Rather than your average "traditional monsters" (such as zombies or werewolves), monsters are a bunch of creatures with bizarre forms, with each individual monster differing greatly in physical forms and skillsets.
(To get a good idea of this, simply look at the list of monster characters below and click into their respective ref sheets, and you will find that they all look very different from one another. And that's not even a tenth of the total monsters I have in store!)
Most, if not all, monsters possess superhuman strength, speed, stamina, and also have fast regeneration; every monster also has distinct physiology, which potentially also allows them to perform supernatural feats. Monsters also may or may not have superpowers, or magic, or whatever it is you want to call it, that is completely unrelated to their physiology. Or maybe they don't, I dunno. Solve this mystery and you'll get the Takeoverse equivalent of a Nobel prize or something.
All monsters possess the ability to consume (read: eat) humans in some way, and upon eating enough humans, their abilities - both physiological and superpowers - may get “upgrades” (think some kind of twisted Pokémon maybe). However, consuming humans is not required for monsters to survive; monsters are able to survive with little to no sustenance intake, not to mention human food (such as... uh... wheat...?) is also a valid form of sustenance for them.
Monsters have an extra sense called “affinity,” which allows them to sense monsters and humans and differentiate between the two. This sense works kind of like an aura sense and can go through walls.
Monsters are quasi-immortal; this means that if they are not killed, they can persist indefinitely.
There are decidedly a lot less monsters than there are humans. Monsters typically cannot reproduce on their own (whether sexually or asexually), but rather seem to mysteriously manifest out of thin air (nobody is sure of their origins for now). The amount of monsters manifested in a certain time period is a number that fluctuates wildly and is also very hard to estimate, but so far most researchers believe only around 1~10 of them manifest in an entire year.
Monster characters
Notable characters that are / were monsters include: