I, along with most of the LoL community, have been playing the hell out of URF this past week. I've tried to keep my playtester mindset through the chaos and ridiculousness. Pay attention to what makes a champion fun along with what makes them OP without making them any more fun to play as or against. With that in mind, here are some suggestions for nerfs on the currently disabled URF champions:
1) Ryze and Skarner.
Ryze and Skarner, with their spammable shield/snare and ridiculous mana costs, get plenty of power from URF without their passives. Disable the passive and they'll play the same, still be powerful, but not broken.
2) Soraka, Alistar, Nidalee, Sona, Kayle.
Pretty obvious what's needed here. Reduce healing just like on ARAM. Might want to make it 25%-35% instead of 50% though. The heals aren't *that* OP.
Being able to run anywhere he wants, whenever he wants, and ult over walls every 20 seconds makes him powerful enough and feels like Hecarim. The Hecacopter on the other hand (his Q), is stupid and no fun for either Hecarim or his target. Funny as it is, once the novelty wears off, you realize you have a zero-skill ability that completely negates evasion. Any squishy or low health people can either burn all their mobility to get under a tower where he can probably kill them anyway or just die. If they try to out-maneuver Hecarim under the turret, Hecarim just needs to stay somewhat close to the target, something made even easier by his unmatched speed, and the target dies. I have the feeling Hecarim will be powerful even if you nerf the CD reduction on his Q down to 30%.
The Void Walker hasn't been on URF and there's no one similar to him, unlike Ryze, so this suggestion is going to be less educated-guess and more stab-in-the-dark. I assume the problem was that he was impossible to shake off and stacking the damage from successive ults added up to scary numbers. I'm going to suggest changing his ult to be "can't use while two stacks are active" giving him two jumps- a jump in and a jump out, or two to chase or run -before he has to wait the 12 seconds it takes for the stacks to wear off.
Seriously Riot, you really dropped the ball on this one. I can't believe you nerfed her so little. I suggest nerfing her max health another 0.25. Rounded up of course.