Buff Jayce
His early mana is so bad. 2 abilities and boom, out of mana. If he takes the Tear route, hes utterly useless in lane, and wont get shit for cs. His health/armor makes him die in 3 hits.
Buff his mana and mana regen. Buff his Attack Speed. Lower his Cooldowns. Give him extra armor in hammer mode. Increase his damage when in Cannon mode. Increase his base movement speed.