Innate:Kayn wields an ancient, sentient weapon, that battles with him for control. Each instance of damage against champions causes them to drop an orb that are automatically collected upon leaving combat (including after Kayn's own death), filling a bar above Kayn's portrait.
Once the bar is Full, which scales down with game time, he can choose to either be overwhelmed by Rhaast or expel him to become the Shadow Assassin, based on whether he has damaged more melee or ranged champions, respectively. Once primed, the other option becomes available after 4 minutes.
The transformation can only be performed by interacting with their portrait while on the summoning platform, permanently changing their abilities and granting them Homeguard.
Shadow Assassin: Whenever Kayn deals damage against enemy champions he also deals 12% - 44% (based on level) of post-mitigation damage 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 26% - 43% (based on level) of the post-mitigation damage that he deals with spells against enemy champions.
At the start of the game, it takes 140 Orbs to trigger the transformation. As the game progresses, the value of each orb picked up from the ground is increased, although the number of orbs dropped in combat does not change.
The exact rate of increases is not yet known.
The progress meter above the champion's portrait tracks the highest number of orbs collected between Red and Blue, not the total.
If, for example, you have 50 Blue and 70 Red, the progress bar will be half filled (70/140). If you enter combat with a ranged champion and collect 10 more Blue Orbs, the progress bar will not visually change - as 70 Red is still your highest.
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.
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 (+ 120% 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)
5 / 6 / 7 / 8 / 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 Kayn immune to them for the duration. Additionally, entering terrain will increase the bonus movement speed to 70% for the remaining duration.
Turrets do not count as terrain for the purposes of extending the duration or healing Kayn, but inhibitors do.
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 coded as dashing, so knockdown would stop him from moving (althrough using outside terrain won't be blocked by knockdown).
Kayn can 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.