Veigar is getting nerfed the wrong way
On PBE (which can be changed at anytime) Dark Matter base damage and ap ratio is getting nerfed. Dark matter isn't the problem. It's his ultimate that is an issue. His ultimate has no counterplay whatsoever towards ap mages. With the amount of damage stacked in his ultimate that punishes ap mages for doing good is the problem. The enemy can win lane early and then lose because of how well they did. What I suggest is taking away the 80% enemy ap as damage passive and raising the ap ratio on veigars ultimate. That way, the enemy mages does not get punished for doing well and veigar stands a better chance against ad mids. It's balance from both sides.
