Following up on the previous #flumphening comic about backpacks, the unusual (read: unnatural) anatomy of flumphs would pose other problems. Specifically, wearing and using most magical gear. You can imagine some working, such as belts, necklaces, cloaks, and most wielded items.  Presumably potions would continue to have some effect, and their inhuman biology wouldn’t render the magic ineffective. (I wonder if a potion of healing would give a flumph gas…)

But then one considers other forms of magic items. Boots and gloves are the obvious ones. As are armour. Rings sized for fingers and not ropy tentacles. Hats. Would bracers work or not?