From Dungeons and Dragons: Monster Manual I, the Piercer was a cruel joke to the collection of creatures. It was a Dungeon Master’s evil ploy to reign unholy terror by impaling an unsuspected adventurer below.
“… these monsters are indistinguishable from stalactites found on cave roofs.”
One of many monsters-in-disguise, the Piercer wasn’t received too well by players when seen a second time. Every D&D enthusiast had their own Monster Manual. Through telepathy, every enthusiast let every other enthusiast know they hated them. As a DM, I was sort of intrigued by the Piercer wondering how did it evolve? How does it eat? But when players started looking up each time they walked into any cave, it spoiled the mood from an encounter in a long previous adventure.
Important facts: Piercers have a 95% of surprising you. Guess looking up cowering behind your shield doesn’t help.