Is there any reasons to kassadin ulti to have mana

Because the cougar-bitch is overloaded and mana-free seriously, they need to redesign niggalee

While it's true that kassadin needs buffs, nidalee is perfectly balanced, a bit on the weak side I have to say.

Both Nidalee and Kassadin have had intense balance problems in the past. Not only do you have to preserve the identities of these champions, but you have to preserve balance. And it is really hard to balance champions that easily dart in and out of fights, escape almost every situation due to their obscene mobility, and simultaneously deal tons of damage. You have to gate these champions in some way. You can't have the best of both worlds.