Carl's stockpiled consumable granting temporary invisibility, limited by a per-drinker potion sickness countdown.
Carl had been collecting Invisibility Potions heavily and always kept several on Princess Donut, making them the backbone of the Predator move. He drank four during the approach through Zockau alone — one to enter, one after disarming an alarm trap, and more to cover the alleyway work — and smashed one against Bomo's head to hide the rock monster.
For Donut, the effect lasts about two minutes, but her potion sickness countdown of one minute forty-five seconds means she cannot top off her mana with a mana potion and stay invisible, which is why she keeps two slices of Mana Toast for emergencies. The potions hide a crawler's dot on enemy maps but do not conceal the twin swirling protection shells from The Sledge and Bomo — and they can be stripped outright by a deshrouding effect, as happened when the Grand opened fire.
Small glass potion vials that can be drunk or smashed against a target.
Carl and Donut's primary stealth consumable throughout the Zockau raid.
Also appears in books you've already read — spoiler-safe to their endings: