so, I've seen a lot of debate about just what the threshold for monsters should be when dealing with human-like beings, I have a suggestion or two of my own on the topic.
For human-like beings who have never been of the Homo Sapien race we can safely add them but I'd like it if these are kept to more fantastical takes (such as the type of "humans" you'd find in medieval bestiaries etc) as well as having at least one supernatural power that can't easily be explained by science.. I'd also think it wise to keep to largely neutral or evil characters in this regard so we don't end up having Superman, the Flash etc on the wiki..
so for example with Marvel's mutants, we can have the human-like mutants that are villainous (Magneto etc) but the heroic ones (Jean Grey, Cyclops) are best left either on Heroes Wiki or Marvel Database (or DC Database for DC's closely related "Meta-Human" concept).
for characters who deviate significantly from human appearance (Nightcrawler, Beast etc) we can have both villainous and heroic characters as they safely fall under "monster" by virtue of their appearance (and again supernatural powers).
The supernatural part is vital, under no circumstances should we have deformed humans like Quasimodo or Elephant Man on the wiki unless they are supernatural in some way (for example the Peacock Clan from X-Files while deformed humans have many traits that make them "monsters", such as a lack of pain, tremendous strength and a beast-like mannerism beyond simple deformity).
For empowered humans (or former humans) I'd follow same rules as above, the less "monstrous" the appearance the more you should look to the mannerism of the character, focusing on the eldritch, evil or inhuman personality of the character (though I stress again we must always have a supernatural element, even with aliens etc, they need to have at least one ability not easily explained by science).
The more "monstrous" the appearance the less we need to worry about the morality part (thus we can have "good" monsters quite easily), this is to prevent many superhero character appearing here unless they are valid (for example Spawn is fine, Batman is not).
I'd also like if gods are kept to monstrous in appearance or mannerisms, that way we are not adding entities that are better suited elsewhere (for example Odin, Zeus, Ra etc are usually depicted as fighting against monsters and are larger-than-life humans, despite their great power), so gods could follow the same rule as above (the more "human" the god is in appearance the more we need to decide if it is the god's mannerism that makes it "monstrous" (cruelty etc), the less "human" the god is in appearance the less we need to be concerned (for obvious reasons).)
For objects of current real-world worship such as God I would greatly prefer if we stuck solely to fictionalized takes of them so as to respect said spiritualities (this does not apply to religious critters like angels etc as they are not held (by in large) in same reverence as a monotheistic deity).