Senna

Innate - Weakened Soul: Senna's basic attacks on-hit and ability hits against enemy champions apply a stack of Mist for 4 seconds, modified to 0.75 seconds if Senna starts winding up a basic attack on them, and limited to once per target per cast. Subsequent hits will collect Mist and deal bonus physical damage equal to 1% − 10% (based on level) of target's current health, rendering the target immune to further Mist infliction for a few seconds. This damage applies life steal at 100% effectiveness.
Enemies that die near Senna may spawn a Mist Wraith from their corpse. A Mist Wraith lasts 8 seconds and Senna can basic attack or hit it with Piercing Darkness or Dawning Shadow to kill them instantly, granting her 8 and collecting their Mist.
Enemy champions and large monsters will spawn a Mist Wraith.
Epic monsters will spawn 2 Mist Wraiths.
Minions and lesser monsters that Senna kills have a 8.4% chance to spawn a Mist Wraith.
Large minions that Senna does not kill will spawn a Mist Wraith, while lesser minions and lesser monsters that Senna does not kill have a 28% chance to spawn.
Lesser minions executed by an allied champion's Quest item have a 8.4% chance to spawn a Mist Wraith.
Mist: For each stack of Mist, Senna gains 0.75 bonus attack damage. For every 20 stacks, she also gains 20 bonus attack range and 8% critical strike chance. Additionally, every 1% critical strike chance in excess of 100% is converted into 0.35% life steal.
Innate - Relic Cannon: Senna's basic attacks on-hit deal 20% AD bonus physical damage and grant her 10 / 15 / 20% (based on level) of the target's movement speed as bonus movement speed for 0.5 seconds. This damage applies life steal at 100% effectiveness.

From the twin barrels of her Relic Cannon, Senna fires a unified beam of light and shadow through a target, healing allies and damaging enemies.

Senna sends forth a wave of Black Mist. If it hits an enemy it latches onto them hungrily, rooting them and everything nearby after a brief delay.

Senna draws the Mist she has stored in her weapon into a storm around her, embracing darkness and becoming a wraith within. Allies who enter the area are camouflaged and also appear as wraiths as the Mist shrouds them. Wraiths gain increased Move Speed, are unselectable, and hide their identities.

Senna calls upon the relic stones of fallen Sentinels, splitting her relic cannon into a holy array of shadow and light. She then fires a global beam that shields allies from harm, while damaging enemies caught in the center.