I recently read Shards of Honor and really liked the unnamed blood-sucking jellyfish, so I tried my hand at making them into a DW monster:
They drift through the air like dandelion seeds, their transparent, globular bodies sparkling in the sun. When unexpectedly and with a sudden purpose, the lead jellies dart downward followed by the entire flock. They land with a jabbing sound upon an army of goblins and begin to fill with blood. The soldiers scream and beat at the parasites, but there are too many. One of the goblins, its body covered by the now-red orbs, manages to reach the campfire. Burning stick in hand, it punches one of the jellies. Boom! The creature explodes along with the goblin and anyone near it.
Instinct: To drink blood
Tiny
Flying, Horde
3hp, 0 armor
Horde
Close, stinging tentacles (d6-2)
Special Moves
Latch onto a target and drink its blood
They’re everywhere!
Explode
https://herethestorybegins.wordpress.com/2016/04/18/flying-vampire-jellies/
Terrifying! I could see a group of them being called a mirage, since they would probably make someone think they are seeing the “heat coming off a highway” effect from a distance.
“They’re everywhere!” might be my favorite monster move ever.