Monsters:
Alien (impulse: to change the environment drastically and irrevocably)
Apex Predator (impulse: to consume and sustain)
Beast (impulse: to spread destruction and chaos)
Horror (impulse: to inspire awe and terror)
Hunter (impulse: to eliminate all threats, real or imaginary)
Shapeshifter (impulse: to deceive and spread lies)
Undead (impulse: to remind of inconvenient truths)
MC Moves for Monsters:
* Hint at its presence.
* Display its full might.
* Get a hold of something, disregarding anything that might interfere.
* Crush something, annihilating it completely.
* Make a rash and sudden action, devoid of human emotions.
* Execute a carefully hatched and unmistakeably immoral plan.
* Gloat, possibly revealing a weakness.
* Dictate somebody's behavior: charmed, frightened, enraged.
* Have its behavior dictated by someone else: tamed, provoked, manipulated.
In Apocalypse World, the moral high ground probably got nuked along with the rest of the world. There's no more good and evil, right and wrong; only bigger gun and smaller gun.
Sometimes, though, we want to re-tune our moral compass, be reminded that there's wrong and there's plain wrong. This is where the monsters come in. Unlike grotesques, the monsters are fundamentally inhuman, even if they do inhabit a human body.
I came up with the monsters for my PG-13 game, where the players (and later the MC) were clamoring for glowing purple worms, skeletal dinosaurs and other exotic inhabitants of the wastelands, and the moves for warlords and brutes weren't quite cutting it.
The monster moves were successful, but I always insisted on no more than one monster per front (including the home front). More than one might work, but I sincerely doubt it. Anyway, I'd love some feedback.