In patch 10.12, Yuumi was still one of the hottest support champions in the meta with top-tier win rates and bans. However, in patch 10.13, you should absolutely avoid picking Yuumi because the “Queen” has been hit hard by a brutal nerf from Riot Games:
“We have nothing but love for this kitty, but Yuumi’s energy consumption is being resolved far too easily with the energy regeneration system. We fear this needs to be stopped.”
The details of the adjustment indicate that Yuumi’s Ability (E) energy cost has changed from 100/115/130/145/160 to 40/45/50/55/60 (+15% of maximum mana). This change means Yuumi is always energy-starved if she maintains her usual E buffs for teammates. This single nerf has caused Yuumi to plummet from a top-tier support to the bottom of the ranked win rate chart, even though patch 10.13 was just updated a day ago:
Yuumi ranks 4th in the lowest win rate champions in the meta
Currently, the most supported idea in the community is to change Yuumi’s E mechanic: to allow this E ability to stack, providing the most buffs on the first link with an ally. Continuous use on the same ally would consume more energy and have less effectiveness. This would create opportunities for enemies to punish Yuumi’s mistakes, while also allowing Yuumi to provide more health and attack speed buffs when switching allies during team fights.