The enchantment for cross bows and possibly bows but if I'm right it only goes on cross bows is the best enchantments for cross bows and possibly bows. The enchantment allows you to hit 1 extra mob per level of the enchantment if the mob/mobs are in a line. But you may be thinking. "Colatrix, why would I want that mobs almost never in a straight line. Why would I want that?" The answer is basic, the arrow goes THROUGH the mob, not into it, so you can hurt the mob and then pick your arrow back up after being shot. If the arrow has an effect on it before fired, it still has the affect and whatever it hit also has the affect.
Indeed, Crossbows are the only tools that can have the piercing enchantment in MineCraft, but it would be nice having the Crossbow's unique enchantments such as multishot and piercing in PoC.
Their is piercing. I passed while enchanting books I didn't get it because I didn't remember that you can pick your arrow up after dropping it I thought it just made mons behind the shot mob get hurt I didn't figure that I would get the arrow till I looked it up