What if Event Horizon was an expanding stun from the center of the ability?
So people are really angry about the recent (potential) changes to Event Horizon, and I can understand why - Veigar is now incredibly weak against Champions with movement abilities who can escape before the stun goes off, whilst Mobile-less Champions are still screwed and can't really do anything against it.
So I had an idea on how to change Event Horizon in a way where there is a little more "actual counterplay", and will let Veigar fare a bit better against mobile champions whilst not making him the huge threat he is against immobile champions.
My suggestion is this - On initial cast have the stun be based around the center of the ability, and over the abilities lifetime have the stun expand in a ring that reaches the "gates" of the ability (such as it currently does now.)
This I feel could be a potentially good change as it still lets him use the ability effectively against mobile champions (he would not have to wait for them to burn their dashes or leaps, though in exchange he has to trap them in the gate) while making it a bit easier for immobile Champions (who can now safely farm against Veigar now that his big AoE stun can't immediately stun them at the bare edges, meaning he can't stun you then casually use W-Q-R to kill you.)