Lost to a Yellow Stone

From itch.io:

The Players are tasked with the retrieval of a potent and rare yellow gem, which is used in high-level Alchemy. It was stolen from the local Arcane Academy weeks ago, and the players have tracked the movements of the thieves to a system of caves below tall, rocky, mountains.

These caves, however, are home to a particular species of Drowshrooms that fill the air with spores that make whoever breathes them drowsy and lethargic. This is the perfect environment to thrive for some flesh-eating snails, too slow to chase their prey in the open. These Drowsnails adapted to the spore-filled air and even attach small Drowshrooms to their shells.