The floor's ubiquitous common scroll granting brief underwater breathing — a not-subtle hint of a water-heavy level.
Scrolls of Water Breathing flood the party's boxes — Donut's, Katia's, and Carl's alike — letting the user breathe underwater for (Intelligence x3) seconds. Mordecai reads their abundance (like the antidote potions) as a broad hint that the fifth floor is water- and poison-heavy, making them this floor's version of the torch and bandage. To Donut's horror they underline that swimming is coming; Mordecai promises to brew a proper water-breathing potion if he can find materials.
A common scroll.
A common consumable and an omen of the floor's watery, dangerous quadrants.