Page 35 of the 5th ed Monster Manual brings us to the bullywug, a boring petting-zoo-people reskinned goblin which should not exist. They should be replaced with the blindheim, from the old Fiend Folio. It's a frog guy and it looks at you and you go blind because they looked so fucked up.
They are a kind of Slaad--the gods of frogs--and come in all sizes and kinds--any sufficiently pious frog or toad (they aren't biologically distinct) can be transformed into a blindheim via acts of consequential service to their kind.
The Cambion in classic demonology is like a changeling baby but with succubusses (which is more fun to say than succubi). Ever since at least the original Monster Manual 2 it has always grown up to be yet another generic horned devilperson that can do things like charm or poke you with a spear.
Their conception is according to at least one source weird:
1. Succubus fucks guy, gets cum.
2. Succubus gives cum to incubus.
3. Incubus puts cum in human woman.
Between steps 1 and 2 and steps 2 and 3 there are several intriguingly tasteless adventure hooks or hentai plotlines. The only interesting thing I found in research about it after it's born is that it's extremely heavy.
Cambions are not found as adults--as adults they either become full-on demons or grow into tieflings (so you can have PCs whose "parents" are succubusses which is fun). As an encounter, what you get is a gross child between 1 second and 5 years old--generally a punishment for excessive lustfulness.
The Cambion has a fuckton of hit points (82, like it says in the book) and good AC (19, like it says in the book) it bites for like d8+4 damage with its creepy teeth but its main gimmick is heaviness.
It gets heavier the longer it's in one place or in contact with a given creature, and cannot move except of its own volition.
The goes in for the kid-grapple (I would say it charms you into a hug, but I already used that for lava babies) crawls onto you, begins to bite, and each round grows heavier--the first round it requires a strength save of 18 to stay upright, then 20, then 22 etc. All the while it exerts pressure on the floor equal to an attack with a strength equal to the save--shattering wooden planks, then stone tile, until it begins to be so heavy it will actually pull you into the ground, through all the dungeons of the earth, and down to hell to meet its parents.