You want a list ? Fine I’ll give you mine 
Alani > nerf her healing and slightly her damage output
Ambra > buff a bit her healing and give her some slow or blind.
Caldarius > could use a slight increase in damage (on his weapon)
el dragon > his ult should be faster to activate but deal less damage on basic attack once activated. It’s a risk to use it but the reward is way bigger than the risk.
Galilea > rework her “pull” helix so it doesn’t work on everyone she’s not aiming at.
Ghalt > his ultimate feels like crap to me, it looks like he deals less damage with it than with his basic attack, that could use a buff. (but I’m not really sure, that could be my aiming that s*cks hard)
Isic > he could use a minor decrease of his weapon damage
Marquis > once he has 2 or 3 specific helix he’s soooo powerful, I think he deserves a tiny nerf of his damage (not too much)
Melka > her poison damage should be toned down a bit
Miko > give her a charge for her healing like for kleese’s taser.
Orendi > buff a bit the damage of the pillar, it feels really weak
Oscar mike > rework the helix next to the napalm, nobody who knows how to play mike uses that one because it’s cr*p (and a tiny reduction of the napalm damage would be great…)
Phoebe > reduce her slow from 6 to 3 seconds.
Rath > Allow people who’re knocked up to freely move their crosshair, especially down in order to see where rath is going. There is no reason for a knockup to also stun.
Thorn > decrease slightly her damage & her AOE damage.
Toby > rework his ultimate, it’s garbage and even his lvl 10 helix are both garbage. It’s slow to use, not efficient regarding the damage, and makes you vulnerable.
Foxtrot > allow him to reload during his ultimate to stop it. His sticky nade could use a buff in damage, it’s fairly hard to aim and deal tiny damage compared to mike’s grenade which is easier to aim and deal more. (I think ?)
The ones I don’t talk about are fine in my opinion, or I never played them or experienced too much against them.