IMO the Cold Nova needs to be scaled down. At that point in the game you don't always have very good movement, but if you're slow enough you're basically guaranteed to die every time the Cold Nova rounds start going off. My friends and I struggle with him way more then any other boss, but at this point we've familiar with his patterns (AFAIK) and those Cold Nova blasts guarantee we lose way more lives with him then the other bosses. I think if Cold Nova was scaled way back he'd be a lot more balanced, but maybe we're missing some sort of tip that's relevant? I know it took us a long time to learn how to watch for the KoTL blast effect.

I know Aghanim's has a similar "get good movespeed or die" but he's the last boss, Balanar is too early to have to prioritize BoTs like that (plus I usually try to avoid BoTs and pick-up a T5 boot instead, which is not an option for Balanar).