Casting spells grants a stack of Arcane Mastery for 12 seconds.
At 5 stacks, Ryze becomes supercharged for [3 and going up to 4/5/6 based on ult rank] gaining a shield that blocks [25 + ~5 per level] (+8% of his maximum Mana) damage and causing his spellcasts to reduce the cooldown of his other spells by Overload's cooldown (4 seconds base, IS decreased by CDR), to a minimum of 0.25 seconds.
Ryze's abilities gain additional strength based on his maximum Mana."