“ Foot Coral. It attatches to a foot like moss, almost gluing itself to an organism. It gets its food supply from the ground, and does not leech off the host in any way. It is not a malignant organism, and is entirely harmless. But it only grows on human feet, and even then, never on the left foot. An organism that it grows on can feel touch through the coral, but not pain. Removal of the coral is painless, but why would you want to?
Texturally, if fells like a dry, non slimy amoeba.”
“ Adventurers are to capture an unknown monster for examination (for a sage or wizard) but they are themselves captured by the monsters, and researched.”
“ A casual remark by one of the party about something met on a previous adventure leads to a summons to and grilling by the Mages' Guild (or equivalent), probably resulting in an expedition back to that area to recover the things for study by the Guild. The party's presence will be 'requested' for this expedition.”