Yuumi Quality of Life Possible Improvements

For her Passive, I think it would be nice if you could gain the passive from things like baron/dragons/turrets. mainly useful for getting ardent and it would give her a more reliable way to get her passive mid-late when walking up and auto attacking an enemy is far more risky when 5 people can jump you instead of 2-3.

Q i think is alright where it is i have to play more to see how the slow is after the hotfix

For her W, First, I think when you're attached to someone, your max w range to transfer to someone else should always be visible (similar to Rakan after his first cast of E). This will also help you keep track of where you are in a teamfight because you can find the center of that circle. Second, pressing W while out of range of any teammate should disconnect you from your current teammate (currently it shows the cast range of W and does nothing besides that, which wouldn't matter if point 1 happened), otherwise you have to actively look for a spot in the range of w so you can disconnect to auto attack players/turrets. Third, it should be way more obvious who you are attached to. One possibility is for the person playing Yuumi to have a green outline around their champion, (not their health bar but their character model) the health bar change is not visible enough in a pinch. For example when three allies are stacked on top of each other and your adc is low on health and you don't remember which person you last attached to, if you choose to W the adc and you were already attached to them, you will detach and have to reattach in order to heal them leaving yourself out in the open giving the enemy a chance to burst you down. If you just assume you are attached to adc and heal, then you may be on the full health tank and your adc gets no healing and dies. Side note, maybe leveling up w could increase the range you can hop to allies to give maxing it a greater impact but that's not really a QoL and more of a balance thing which I am not as knowledgeable about.

E I think is fine as well

For her R, It would be great if activating ult during it's channel would cancel it. It feels bad to miss or they dash/flash to the side so you just sit there for 3 seconds waiting until you can Q and auto again. Another possibility is to let Q be cast during ult which may be too strong also feels weird that your ult can be interrupted , maybe this is to dissuade Yuumi from using it not attached but it doesn't feel good.

Besides that i'm having so much fun on this champ