After finishing grinding out Neeko to M7 on my main account, I've been trying to do the same with Yuumi (currently M6), and she's been one of my main supports since she came out live. Here is my feedback on her:
The mana back on passive is very welcome.
Her Q could use a little more slow. The slow is so little in such a short time that it can barely be considered a form of CC. Trim a little damage off at higher levels and have the slow scale as she levels or puts points into it.
She also didn't need the bonus attack speed on E, but the mana cost is way too high, especially early game. Taking away charges is welcome, however. Lower the mana cost slightly early game. E heal effect and cooldown should be reduced slightly late game so she can plan when to hop between teammates.
Nothing to say about her R.
Alright, now is the main part of the feedback, her W:
I'm fine with her not going with Teleport and the W windup is a little bit clunky. I'm neutral on the windup and will need to play a few more games to determine how to feel about it. Riot, if you really intend on keeping the W cooldown when she gets immobilised, don't let it refresh. So many times I could have gotten out of bad situations but I couldn't because of the 5 second timer refreshing before it even hits 0. If you want to punish a Yuumi player for making positioning mistakes, then that's great. But the 5 seconds shouldn't repeatedly refresh over and over, it completely negates the mana back on passive because it gives us no incentive to even risk getting our mana back.
What are some alternatives to the proposed kit she has now?
* If you so intend on keeping the idea of putting her W on cooldown when she she is hard CC'd, then at least have it scale down as she levels up or as she puts points into it. Players will have to choose between 3 situations
* If they max Q first, they will have damage, but they exchange the W CC reduction and the E heal increase for it
* If they max W first then they will have the CC cooldown reduction but will lack damage from Q or heal from E
* If they max E first they will lack damage/utility from Q and the CC cooldown reduction from W
That should in turn open up paths to different Yuumi playstyles and she can adapt more easily to the flow of the game
Alternatively, should the W cooldown timer be removed entirely?
In her current iteration on live, Yuumi can be CC'd any time she is outside of her teammate or if you catch her while flying. The hard part is done; you've punished Yuumi for mispositioning and caught her. The enemy should be looking to kill Yuumi quickly before the CC wears off. It should be easy right? The reason why playing against Yuumi can be frustrating is because players don't capitalise on catching Yuumi. Even if the entire enemy team is there, through smart plays, you can easily kill Yuumi while she is CC'd given how squishy she is. If you CC Yuumi but don't attempt to do anything about it, why complain about her being untargetable? The enemy team shouldn't be given a handicap (which is the 5 second W timer) because they couldn't kill an already caught Yuumi.
That's all I have, so please let me know what you think! Constructive criticism is welcome and I'd love to be able to bounce ideas back and forth with someone on the proposed kit.