Well,this is actually a rare example of a good yuumi main.They did some crazy calculations or predictions there. As a yuumi main myself, im really impressed by how that person kept in mind literally everything that was goin on
- Higher mana cost for higher heal - Now she has to play aggressive and detached to get mana back and be useful - She can't easily escape during teamfight and you can actually punish her when she makes mistakes Atleast it is healthier to play against her now ... Unfortunately she will be nerf again I think because her synergy with the Athene's unholy grail is too strong ! One E + the passive of this item and your adc get all his hp back.