Invisible Madness-faction saboteurs who infiltrate the castle base using tech-based cloaks the anti-magic charms cannot detect.
During the surprise assault on The Castle, the Monkeywrenchers form one of three enemy elements inside the camp, alongside The Reavers paratroopers and mages hijacked by Gondii brain worms. Their invisibility comes from prohibitively expensive real-world tech cloaks rather than magic, so the base's anti-magic bubbles never register them; Donut's sunglasses on the heat setting are one of the few reliable counters, and Carl kills one with a thrown Banger Sphere.
The Monkeywrenchers turn out to be a mixed bag of hired talent wearing Madness masks — one killed at the barracks mural proves to be a soother mercenary, and another is a Dreadnaught in a Viceroy mask. Splash Zone notes he has yet to see a genuine The Viceroys among them. Their real job is not to win but to pin the defenders in place until the main northern force arrives, and they wane and flee once Tina is unleashed.
Cloaked and effectively invisible until damaged, at which point their outline flickers into view; each wears a Madness mask that falls away in death, revealing soother mercenaries or other hired species beneath.
Invisible vanguard saboteurs whose job is to pin the castle defenders while the main enemy force closes in.