Barnacles

These inch wide crustaceans cling to damp stonework or submerged surfaces. If a creature brushes against them or steps on them they flip round and latch on. Their shells are hard as granite. They cling on very tightly and can only be chiselled off with sustained effort and tools (at least a dagger and something to use as a hammer).
Every turn spent in a barnacle-choked environment burdens you with enough barnacles to fill an inventory slot. It takes a full hour to remove them, or half that with perfect tools. Once removed they can be cooked to make a nourishing chowder that replaces a ration.
Monsters that have spent several months in the environment become fully encrusted, slowing them dramatically, but giving them improved armour.
(This is an expanded version of a post I made on Mastodon)
Waders

Malacular waders are 4 foot high birds with oily green feathers and an evil grin. They wade slowly round barnacle-choked environments emitting piercing shrieks that can be heard from some distance away.
Their shrieks make the barnacles release their hold; the wader then gobbles them up. They will fearlessly eat off encrusted creatures. If threatened, they increase their volume, and can also deal a vicious bite with their beak.
Their cries mimic a forgotten name, said to be that of a demon of broken oaths, a spirit of unbinding, unlocking, and revealing of dark and suppressed secrets. As well as ungluing the barnacles, their cry can open locks, buckles, and knots, loosen false teeth, unbind seams in clothing, and even unravel minds.
Whenever the wader shrieks within 30 feet, each creature must save vs taking 1 “unlocking damage” (UD). If the wader is angered or within reach the save is harder. More distant shrieks (audible within a few minutes walk) require a save once per turn.
Effects of “unlocking damage”
- -UD penalty (max -6) to actions due to clothing, buckles, etc. falling off and needing to be held in place.
- Additionally, if you reach for a specific bit of gear, roll UD-in-6 chance it has fallen off without you noticing.
- If you flee, when you catch your breath roll UD-in-6 for each item slot to see if it is gone.
- At 3 UD, all barnacles fall off.
- At 6 UD, all equipment not held and all clothing falls off.
- For each point of UD beyond 6, minds start to break down: If there are any suppressed secrets they surface. Otherwise, roll UDin20 each round to take any actions as opposed to having a breakdown - raving, collapsing, crying.
Unattended doors, chests etc. have a 1-in-6 chance of unlocking every time the wader shrieks. Consider adjusting this to 1-in-10 or 1-in-20 for very hard locks.