(thanks dechta for the perfect emote for the feelings im having.)
I GAVE UP ON THIS. THEN I REALIZED THERE IS ACTUAL FUCKING PRECEDENCE! SO I'M FREAKING BACK!
The main issue was that supposedly there was no way to know if the target shes about to hit is marked BUT!
Kai'Sa, has a special animation when autoing targets with 4 stacks of her passive. This means Riot could actually do this and has the tech for it! There's actual precedence!
Let's get right to it.
Lux should use her Crit animation when autoing targets marked with her passive, illumination.
For those of you who don't know her crit animation is her twirling her wand, it's just about never used, despite this she has a quote about twirling her wand which she almost never does.
Video of her crit.(and almost all other base skin crits if you're interested)