I'm not sure if I like these changes

Especially not the proposed stuff for Mordekaiser. Why is his damage being lowered? He isn't a tank and he doesn't function as one, and his sustained damage is hardly at par with a lot of other picks (who actually have sticking power). If you're going to make him all about sustained damage then he needs a way to stick to targets. A slow, a stun, literally anything to stop people from just outrunning him so he can keep whacking you. I honestly can't see any reasonable way this will work without more changes, but this feels like pretty awful compensation.

Mord's got literally one approach to bursting you and needs a lot more than other champions to actually do it. He can walk up to you. That's it. He probably needs more than one rotation to 100-0 you with QER as well, and he's got an isolation requirement to make his Q actually hurt.

What actually are you doing with him? Making him a sustained threat is basically making him completely worthless unless he actually gets the chance to be a sustained threat.

And for Veigar...

Q - Baleful Strike Changed to a skill shot that stops on the second unit hit Grants 1 AP for each unit killed Range increased to 850 from 650 Cooldown changed to 7/6.5/6/5.5/5 from 8/7/6/5/4

Why is the cooldown up a second? It's his only form of sustained damage and you've already made it really unreliable, why are you giving it more downtime on top of that?

I guess the skillshot is nice since you can hit 2 people, but it still goes to the same range (no extension from hitting/killing a unit). I just hope this doesn't turn him into a siege mage, because they have to be the absolute worst archetype there is. Being able to W waves and get more AP out of it is a welcome enough change. R - Primordial Burst AP Ratio reduced to 1.0 from 1.2 (Ratio on enemy's AP unchanged) Mana Cost flattened to 125 at all ranks from 125/175/225 Cooldown reduced to 120/100/80 from 130/110/90

Why are you keeping the most unfair aspect of this ability? He still gets to one-button delete APs late game, but now his newly unreliable combo now does a good chunk less all game to people who build AD. Why didn't you just get rid of the enemy AP scaling altogether and buff up the universal ratio?

E - Event Horizon Has a 0.75 second delay with a warning particle before the walls appear Mana Cost decreased to 80/85/90/95/100 from 80/90/100/110/120 Cooldown reduced to 18/17/16/15/14 from 20/19/18/17/16 Range increased to 700 from 650

I don't like this. He needed his E as a safety net with all the already obnoxious mobility in the game , and the rest of his kit wasn't really changed to make up for power being taken out of it. Speaking of..

W - Dark Matter Mana Cost reduced to 70/75/80/85/90 from 70/80/90/100/110 Cooldown reduced to 10/9.5/9/8.5/8 from 10 at all ranks

I would've preferred the delay being shortened even by a little bit. If you're going to make the combo less reliable then the abilities should be functional on their own.

And lastly, there's no passive changes. There should be a new passive; Veigar deserves one.