Yuumi
Alright it's been a little over a week and I want to get my thoughts on her into writing. TLDR: Having a champion that depends on teamwork isn't going to make the dream work in soloq.
First off: As is this champion is always going to be exclusively proplay/extremely high elo. The communication and work required on the ADC's side makes her suboptimal. The numbers that would make her winrate anywhere near decent in soloq would make her pick/ban every game in proplay. Her kit's built around working with allies and even with a duo partner you're never going to get the maximum usage of her kit outside competitive. But what changes can be made to open her up to more than the top .01% of League players?
Passive: B/B is very well adjusted for laning phase with adc but in a teamfight it's nigh impossible to get off your frontline long enough to get off an auto without being blown up, especially since Yuumi has the lowest health in the game and doesn't go untargetable until she finishes reattaching. Proposed SoloQ Fix: Make Yuumi able to queue and execute autoattacks during the detatch animation. She needs to be able to queue the reattatch as soon as she's off the champion and can't afford to eat 800 damage+ for a 300 dmg shield on a character that already has thousands of HP. Considering how animation canceling doesn't do much for her I don't think you have to start worrying about on-hit Yuumi builds but even that'd be better than a champion only pros can do well on.
Q: Yuumi's Q is the first controllable skillshot in the game, but only when you're attached. The slow it gives and its low cd makes it a walk in the park to run down enemies. It follows flashes/dashes, goes through walls, cuts corners and dodges minions, but your allies have to be chasing the enemies for it to matter, but more on that in a second. The range on this ability is potentially massive- the circle of range moves with the champion, like Zoe. Except unlike Zoe, you depend on your allies movements to make it connect. If your adc doesn't move with you to let your poke reach the enemy champions during laning phase, you're basically useless. Thankfully ADC's are pretty good at catching on to how to help you connect Q's. Soloq isn't using its potential to run down solo targets well enough right now but that potential would be realized if Yuumi became popular enough for allies to learn what she can do. Proposed Fix: Rioters, you need to choose what you want this ability to do and execute on that. If you want it to do damage then up the ratio and she can be a pretty good poke sup that can hide on frontline to keep poking. If you want it to be used in making picks then up its projectile speed, slow %, or make it a root. Bottom line here is you need to cut amount of teamwork required to happen between Yuumi and allies- I don't mind being shackled to my frontline but if they're not seeing picks and scenarios the same way I am then I become useless.
W: I'm not going to focus on attach/detach because its so integral to her kit that I've already talked about it in her other abilities. The adaptive power sharing is something that can be talked about because of how deceptively useless/powerful this is. Yuumi's AP ratios are bad so Yuumi can't build full AP but then she's not sharing power with her ADC since there is no 'base' bonus to either party's adaptive power. On a sidenote turrets 3 shot her. I understand she can't be allowed to poke for free but being unable to ult until after the initiation is so bad for the cc chain because instead of wombo'ing by slowing them into your team's main cc so that you can land the snares as the big cc ends, the enemy gets to move which lets them counterengage or whatever they want. Proposed Fix: When Yuumi draws tower aggro, direct it to the champion she's attached to. This lets her really help her primary engage while keeping her adc in check if she wants to poke enemies under turret during lane. This is potentially controversial that other players can be forced to pay for Yuumi's agression, but she's meant for late fights instead of early poke under turret so let her function in a way that lets her dive and initiate with her team.
E: You have to build Athenes and charge it up to heal a meaningful amount. A big issue with this is that building AP puts most of the power into its movement speed bonus. The biggest problem here is that it's a catch-22 with saving allies- if you need to get to them in a hurry you really ought to use at least one charge to get there faster before they die, but if you get there without two charges they're probably still going to die anyways. Also her auto range is way shorter than her q range so you're probably going to have to pop off them right after attaching and healing them so that you can get that shield on them too, so you still might kill yourself then while trying to do that or you can die after your ally dies from a lack of shield. Proposed Fix: Up the heal with % missing health. She's meant to ride with the frontline so she need to be able to actually heal them for a meaningful amount. Right now people are doing this with Athenes and it's not awful, but her reliance on building this item has created some unforseen design space that could be used to give her more power while doing this utility/low-AP build, or make her less dependent on Athenes so you can build a different item. Please.
R: It's so unforgiving if your allies don't position in a way that's good for letting you get your ult off. It also doesn't do much damage for the positioning required. There is no proposed fix for this, but if you feel like changing the AP ratio for design space or to give her the ability to do damage in teamfights, noone's really in love with this current version.
Although I talked about each ability one at a time, I also have this pipe dream where Yuumi's W active becomes her passive and her current passive becomes a W- an active shield that scales with max HP, and an increase her E's heal when she only has one charge of it so that she can make saves that she has to blow one charge to get over to. More of an AFK style but she gets bursted so easily that she's already playing it.
Summary: It kind of feels like Riot wasn't really sure what they wanted Yuumi's niche to be so they made her a jack of trades. Of course, who could've predicted how this would turn out on live servers but now I feel like its time for the Yuumi team to gear up and nail her position to an archetype that a wider player-base can find success with.
I'd love to hear other ideas, congratulations Riot for making a champion that can use cutdown to do as much damage as a keystone.