Adapted from a delightful old d&d monster that was sadly forgotten. I think she’s a perfect fit in DW.
Solitary Tiny Devious
Sting (d8 – 2) 12 HP 2 Armor
Special Qualities: Flying, Weakens Spells, Visible Only To It’s Host
These big dumb flies are the worst. They will magically bond themselves with the strongest spellcaster they can find, siphoning energy off all the spells they cast. You can’t get rid of them with your magic because it eats those spells right up. You can’t get your friends to help because they don’t even believe it exists! When you become the crazy guy that blames their inexplicably shitty spells on googly-eyed mosquitoes, this loathsome parasite might be the only friend you have left.
Instinct: To feed.
*Establish a bond with a stronger host.
*Feast on magical thoughts or energy.
*Keep the host safe.
While the magebane is bonded to you, you have this move.
When a spell is cast under a magebane’s bond, the magebane gets healed d4 damage and the GM chooses one:
*Any numerical damage caused or healed by the spell is halved.
*The spell affects less than you wanted.
*The spell’s effects will be dismissed under an inconvenient condition.
*The spell takes a few crucial moments to take full effect.