it means that on occasion your pet may cast a 0 rank version of pierce on the enemy. this is most notable when they cast a shield on themselves such as if a mob cast a storm shield to protect himself from that type damage, your pet would cast pierce and break it
My pet has a thing that says, "pet may cast pierce," and i have been wondering what does that mean If anyone can help me, i'd very much appreciate it.
It means that your pet may cast the spell Pierce during any battle. It is usually 'triggered' by one of your opponents casting a shield. This is not guaranteed to be cast at any time... just a possibility.