xerath Q

I wanna know why this was literally costing him 0 mana everytime he cast it, I watched it the whole game mana bar would not move down after any cast yet all of his other spells did, I assume this spell has a mana cost but for someone to just spam something over and over again and still have 90% mana is absurd I don't care about the range and hit box but this being a free spell which seems to be on like a 2 second cooldown (exaggeration) is mind boggling