Innate:Kayn wields an ancient, sentient weapon, that battles with him for control. Dealing damage against champions causes them to drops orbs that are automatically collected upon leaving combat, filling a bar above Kayn's portrait.
Once the bar is full 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.
Shadow Assassin:Kayn's basic attacks and abilities deal 12% - 44% (based on level) of post-mitigation damage as bonus magic 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.
Active:Kayn dashes forward, dealing 55 / 75 / 95 / 115 / 135 (+ 65% bonus AD) physical damage to all enemies he passes through before flourishing his scythe, dealing the same damage again to surrounding enemies.
Rhaast: Both instances of Reaping Slash's damage are modified to 50% AD(+ 5% (+ 4% per 100 bonus AD) of target's maximum health) physical damage, capped at 200 / 250 / 300 / 350 / 400 against monsters.
Regardless of the form, both instances of Reaping Slash deals 55 bonus damage against monsters.
Active: After a short delay in which he can't perform any other actions, Kayn performs an upwards sweep with his scythe, dealing 80 / 125 / 170 / 215 / 260 (+ 120% bonus AD) physical damage to all enemies in a line and slowing them by 60%, decaying over 1.5 seconds.
Shadow Assassin:Blade's Reach's range is increased by 200, deals 10% bonus ADbonus damage and the slow decays over 2 seconds. Additionally, Kayn conjures a living shadow at the casting position to perform Blade's Reach in his stead, allowing Kayn to perform other actions.
Active:Kayn gains 40% bonus movement speed, is ghosted and can ignore terrain collision for 1.5 seconds. Immobilizing effects will interrupt Shadow Step. Kayn heals himself for 100 / 115 / 130 / 145 / 160 (+ 40% bonus AD) health upon moving through terrain for the first time and, if he's not in combat with enemy champions, Shadow Step's duration is increased to 5 seconds. Entering combat with a champion after the effect is enhanced reduces the remaining duration to 1.5 seconds.
Shadow Assassin: Casting Shadow Step removes slows, additionally if Kayn enters terrain at least once, Shadow Step will be improved for the remainder of its duration to grant 70% bonus movement speed and make Kayn immune to slows.
Rhaast:Umbral Trespass damage is modified to deal 10% (+ 13% per 100 bonus AD) of target's maximum health physical damage, and heals him for「 70% of the pre-mitigation damage 」「 7% (+ 9% per 100 bonus AD) of target's maximum health 」.