Piercer

Piercers drop from the ceiling, taking your character by surprise. If you are wearing a hard helmet, you are somewhat protected. There are rock piercers (p), iron piercers (p) and glass piercers (p), in order of toughness.

Encyclopedia entry

                   Ye Piercer doth look like unto a stalactyte, and hangeth
                   from the roofs of caves and caverns.  Unto the height of a
                   man, and thicker than a man's thigh do they grow, and in
                   groups do they hang.  If a creature doth pass beneath them,
                   they will by its heat and noise perceive it, and fall upon
                   it to kill and devour it, though in any other way they move
                   but exceeding slow.
                           [ the Bestiary of Xygag ]