Xayah
Passive: Clean Cuts
INNATE: After casting an ability, Xayah's next 3 basic attacks
penetrate all enemies along their path, dealing 100% damage to her
main target and 50% pass-through damage to other enemies. At her
maximum attack range, a Feather will be left in the ground for 6
seconds. Xayah can store up to 5 empowered attacks.
When the passive hits additional enemies, does the other targets take 50% of damage that the initial target took or is it 50% of Xayah's AD?
For example, if Xayah does 100 physical damage + 20 physical damage from BoTRK's passive, would the target take 100/2=50 physical damage or (100+20)/2=60 physical damage?
Best Answer
After doing some research I stumbled upon this reddit thread which confirms my suspicions.
Xayah's autoattacks will still apply an on-hit effect to the her initial target, however all subsequent targets will take damage based on the incoming attack without on-hit effects.
As pointed out in the reddit thread her passive is more comparable to a Kayle E than to a Twitch R/Runaan's Hurricane.
In the case you've described above Xayah would deal 120 damage to the primary target and her feathers would deal 50 damage to subsequent targets.
Please note that the incoming attack could critically strike, resulting in the attack dealing 220 damage to the primary target but only 100 damage to the secondary target(s).