Did it drop onto people? I thought I remembered it not doing anything until people put it on like a hood - although, I may just be misremembering it that way because of the name.
I don't really miss the piercer, anyway. They fall into the category of "screw-you" monsters that I never really liked. "Oh, look, stalactites - screw you, it's a piercer!", "Oh, look, it's a chest - screw you, it's a mimic!", "Okay, certainly the FLOOR is safe - screw you, it's a trapper!" I never dug on that style of monster.
As an aside, "screw-you" monsters are not to be confused with the "screw-your-stuff" monsters. "Boy, I sure like my plate mail - screw your stuff, here's a rust monster!", "Well, at least I still have this swell magic shield - screw your stuff, here's a disenchanter!" Bah, I say!