this is my feedback on kassadin:
Youre creating a disparity between what can kass do and how much resourcess he spend doing that. The damage of his QWE early and mid game is EXTREMELY low to be an assasin, to the point that with zhonyas and rod of ages, a full round of REQW even didnt hit an AD kog maw to half health, only doing like 35 - 40% of his health in that full round, that is an AWFULL damage output for an assasin that have more than 200 AP on mid game. The base damage of his skills is too low, the only one champion that have that low base damage in her skills is katarina, and you did that cuz of her resets, but as far as i know, kass have no resets, and have no low cooldowns in his main damage abilities to spam it, like cassio, karthus or yasuo's Q. With that build at that time (zhonyas and RoA at mid game) usually i can get the caster minions with a single W, now i cant even do that.
but its ok, lets say that is intended and we need to experiment with a straight full damage build (zhonyas, rabadon, void staff), the mana cost of his abilities is too high, you use 2 times your ultimate on mid game, and your mana bar is already half empty, a third one, and youre screwed, the changes to the increased mana cost of his ultimate are way too high, this heavily sever his roam potential, now you need to keep your ultimate with one single charge, past that point, youre losing too much to the reward you might get.
with the current kass state, the problems to the players are this:
If you want to have mana to do your things, you will have no damage to fill your assasin role, you will be unable to beat your lane opponent, and if you roam, you will have not enough damage to have real impact on the lane youre ganking
If you want to have damage, you will have no mana to do your things properly, you will run out of mana too fast, and you will need to go to base very often, losing minions xp and gold, and if you go to gank a lane, you need to go walking (again, losing roam potential)because if you go riftwalking, you will reach the other lane almost oom.
the changes to his W are nice to the opponents in laning phase, no more infinite mana sustain, but is not enough to handle his mana expenditure atm.
revert the incresed mana change to riftwalk: i dont like to be punished for leveling my ultimate, if not, i dont see any reason why i need to level my ultimate, i can reach lvl 18 and i will left my ultimate at level 1, because that way the mana expenditure is cheaper than in levels 2 and 3.
increase the base damage of 2 of his 3 basic abilities: you reduced the base damage AND the ap scaling of all the 3 abilities, so, you need to choose, you want him to be a good early champion, a mid game one, or a late game one, in my opinion, you need to buff the base damage of his Q and W AND the ap scaling of his W, there is no point to have a high risk low reward skill like the current W, and kass should have at least something to poke his oppponents, not a ball that deals a pitifull damage just because is a ranged silence.
Current state of kassadin: urgoth level