How to fix Veigar? Add a "shove".

Like Riot, I did not like that Veigar's Event Horizon was being treated like a strangely shaped targeted ability rather than as a summoned obstacle. Unlike Riot, I do not think telegraphing the ability for 0.75 seconds is the solution.

If I was in charge of the next round of testing on PBE, I would remove the delay, but give the ability a knockback like Trundle's Pillar of Ice that breaks channels and move orders as well as shoving every enemy on the rim of the Event Horizon out of the stun and into the cage. This would mean that while stunning someone isn't a sure thing (since someone has to actually walk into the wall to make it happen) the spell does reliably put people inside the trap.

Combine this with ShortWired's suggestion of making Veigar's spells more effective when fired into the cage, and I think you'd have a nice, flavourful niche for the character as a sadist who traps enemies and then throws magic at them while cackling manically without just being a zero counter play 100->0 nuker.