Lux got a minor buff and shot from one of the current worst supports to top 10.
They Buffed her early game Q. That's literally more or less it. +10 base damage, -2 seconds from cooldown at rank 1. Scaling reduced by 15%(.7->.6).
They also made it so she could flash while ulting, but I don't think that had this much of an effect.
Yet she went from 35th highest winrate supp to 7th.