A Cassiopeia passive that actually synergizes with her design!

So, one thing I always considered interesting about Cassiopeia, pre-visual rework it was more clear than it is now: She is throwing snakes. So i wondered, why not create a passive that's based on something she always had instead of trying to change her completely identity and person?

New passive: Serpant's Reign After every 5th spellcast Cassiopeia's next auto attack spawns a serpent at its impact location. Serpants die after being attacked twice by a champion or tower. Serpant are meele units which seek out champions within visual range of Cassiopeia. Champions bit by a serpant get poisoned for 2 seconds receiving 2*level +0.1 AP magical damage per second. There can be a maximum amount of three serpants alive at a time.