Why can Jayce get this?
Thundering Blow
Mana cost reduced to 40 at all ranks from 40 / 50 / 60 / 70 / 80 / 90.
Meanwhile Diana's W cost 100(!!?!?!?!) mana at rank 5 on a champion that needs to struggle most of the laning phase and needs to build non mana items apart from lich bane.
Not saying she is weak btw just don't get why a ranged/melee assassin like Jayce gets to have his mana reduced when he actually is good with manamune and stuff like Diana gets the shaft?