Veigar doesn't need a "nerf," he needs to be 5 star
First off, his ult can one shot full HP same star opponents with the slightest investment in AP. On top of that, his recharge rate is INSANE and the whole double casting is lolz on him.
Considering he is one of the ONLY full HP predators in the game, he should be rank 5.
He is too strong to be where he is. Way too attainable. Everyone goes veigar just to deny everyone else. He is a disaster when it comes to balance.