Why nerf Gangplank's Q?
Cost down to 40, but no longer refunds mana on kill.
You made farming with Q much more integral to his kit with the silver serpents, now it'll be a mana sink that's hardly worth using for farming over harassment until your barrels kill at least the caster minions.
Hasn't it been well established that it's the barrels making him oppressive? give THEM a mana cost, or make just them not refund mana if he shoots them if he needs to be more mana hungry.