Right now, Veigar is a weird champion. He's a glass cannon that has nothing but damage abilities, except for Event Horizon. In all honesty, if he was a new champion, the ability would feel out of place. And the name doesn't really fit either.
An event horizon, as defined by Google, is _"A theoretical boundary around a black hole beyond which no light or other radiation can escape."_ While you can argue Event Horizon does live up to its name by it having a circular stun gate, I feel like it can be better than that. So here's my proposition.
__E: Event Horizon__
Cost: 65/80/95/110/125 mana
Cooldown: 22/20/18/16/14 seconds
Effect diameter: 600/625/650/675/700
Casting time: 0.5 seconds
Veigar conjures a black hole that activates after 1 second, lasting for 3/3.25/3.5/3.75/4 seconds afterward. After activating, anything (Including projectiles) other than Veigar himself that touches its event horizon will be dragged to the epicenter of the black hole at the same velocity before touching it.
Live projectiles can still deal damage while being dragged to the black hole's epicenter, but will dissipate after doing so.
Enemy and allied champions' movement speed while being dragged will be increased to 600 if theirs is lower than such. Upon reaching the epicenter, they are able to pass the event horizon and leave the black hole.
Enemy champions are slowed by 30%/40%/50%/60%/70% for 3 seconds upon reaching the epicenter.