A licker ghost is a materialised ghost that casually walks around dungeon halls, picking up things at random, and licking them.
Their gait is pretty much like that of Liam Gallagher, a famous bard who may or may not exist in your home campaign.
It's not hostile but will scoff at anyone trying to get in its way - in its own, strange language.
Their tongue - extra stretchy - is actually not part of the licker ghost. In fact, large, parasitic slugs of various kinds have been known to take residence inside the ghost, as a mean to travel around the dungeon quicker. Most of these slugs are poisonous to various degrees, so try to not get licked at.
Some scholars claim that in certain extreme cases, the mouth of a licker ghost is actually a dimensional portal, and the "tongue" is the limb of an horrendous entity located at the far corners of space, where all light have gone out, and fleets of untold horrors are searching for a new home.
On the other hand, why would one believe scholars studying a ghost that walks like Liam Gallagher?