Innate:Kayn wields an ancient, sentient weapon, that battles with him for control. Each instance of damage Kayn deals against champions (excluding damage over time) and takedowns causes them to drop orbs, red by melee champions and blue by ranged champions, that are automatically collected upon leaving combat, filling their respective bars.
Based on the first filled bar, Kayn can either return to the summoning platform to interact with his portrait to either be overwhelmed by Rhaast or expel him to become the Shadow Assassin, or wait 4 minutes until the other form becomes available. The transformation will permanently change his abilities and grant him Homeguard.
Shadow Assassin:Kayn deals 12% − 44% (based on level) of post-mitigation damage dealt against enemy champions as bonusmagic damage, lasting for 3 seconds upon entering in combat with an enemy champion, refreshing after 8 seconds out-of-combat with them or by using Umbral Trespass.
Rhaast:Rhaast heals for 34.5% − 43% (based on level) of the post-mitigation physical damage that he deals with abilities against enemy champions.
Each bar gets filled up completely at 400 points.
Melee orbs grant 2 points per hit and 6 points per takedown.
Ranged orbs grant 3 points per hit and 7 points per takedown.
Each bar has a bucket system.
The bucket starts at 60 points.
Each time an orb is taken the system checks if there's an amount of points in the bucket equal or higher than the amount received from the orb. If there is, Kayn is given an additional orb of the same type he received, while also subtracting that amount of points from the bucket.
The bucket fills by 0.8 points per second if out of champion combat for 70 seconds.
The amount of points received per orb is then multiplied by 3 / 6 / 10 (based on minutes).
The orbs will be collected even if Kayn dies.
The progress meter above the champion's portrait tracks the highest number of orbs collected between Red and Blue, not the total.
The progress bar gives no indication of which transformation is currently leading, which can be difficult to estimate due to the increasing value of orbs over time.
If the bars fully fill at the same, only the bar with the highest excess of points will be considered for the transformation.
Active: After a short delay in which he can't perform any other actions, Kayn performs an upwards sweep with his scythe, dealing physical damage to all enemies in a line and slowing them by 60% decaying over 1.5 seconds.
90 / 135 / 180 / 225 / 270 (+ 130% bonus AD)
Shadow Assassin:Blade's Reach'srange is increased by 200. Additionally, Kayn conjures a living shadow at the casting position to perform Blade's Reach in his stead, allowing Kayn to perform other actions.
Kaynheals himself upon moving through terrain for the first time and, if he's not in combat with enemy champions, Shadow Step's duration is increased. While inside terrain, Kayn's vision pierces all obstructions although cannot see into brush.
100 / 115 / 130 / 145 / 160 (+ 40% bonus AD)
7 / 7.5 / 8 / 8.5 / 9
Entering combat with a champion after the effect is enhanced reduces the remaining duration to 1.5 seconds. The effect also cannot remain active out of terrain for longer than 1.5 seconds.
Shadow Assassin: Casting Shadow Step removes slows and makes Kaynimmune to them for the duration. Additionally, entering terrain will increase the bonus movement speed to 80% for the remaining duration.
Unblocked vision allows Kayn to see the full circle of his vision radius, with the exception of within brush. Note that despite not being able to see into brush, he can still see things beyond the brush.
Effects such as Vayne'sCondemn and Poppy'sHeroic Charge apply an immobilizing effect and so interrupt Shadow Step, meaning as Kayn's opponent you do not have to worry about pushing him to safety.
However, enemies will be notified if nearby terrain is infested if Kayn is within 1000 units - with an indicator being placed on the terrain with a direct line between Kayn and the enemy champion. Slightly less than standard sight radius, but more than the Camouflage detection radius.
While moving in terrain, Kayn is considered dashing, so knockdown effects would stop him from moving.
Kayncan move up to 550 units beyond the outer-edge of the battlefield.
Rhaast:Umbral Trespass is modified to deal 10% (+ 13% per 100 bonus AD) of target's maximum health physical damage, and heals him for「 7% (+ 9.1% per 100 bonus AD) of target's maximum health 」「 70% of the pre-mitigation damage 」.
Spell shields will prevent Kayn from infesting the target, but will do nothing to mitigate the damage once he has already infested them. This is consistent with other delayed-detonation abilities, with the exception of Time Bomb, which was special-cased in V4.13 to behave differently.
If Kayn targets an enemy with a spell shield, the ability will go on cooldown and nothing will happen. Kayn will not dash on the target and then fail, he will simply do nothing.
While often compared to a spell shield, Fiora'sRiposte has been special-cased to instead prevent Kayn from targeting her with Umbral Trespass. If he has already infested her, it will still block the damage as it grants her invulnerability.