Xayah's Ultimate
When I first saw this I figured "okay, that's pretty neat. Kind of a flora parry to juke stuff, but also spits out some aoe damage". Useful for an adc to dodge that one critical ability without burning flash-Merc/etc.
Only afterwards did I read the text and the small note on what is probably the most important and never demonstrated feature, almost as if they were hiding it. "Xayah can move while in air", which makes the ability more like Camile Kick, but also invulnerable like Fizz E, with it being unclear whether she can wall-hop with such 'in-air-ness'.
I don't know how her power scale will turn out, even with this, but it's a very easy detail to miss that vastly changes how her ultimate works.