Piercers are a monster class represented by p. They drop from the ceiling, taking your character by surprise. If you are wearing a hard helmet, you are somewhat protected. In order of toughness, there are rock piercers, iron piercers, and glass piercers.
Encyclopedia entry Edit
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 ]