Heavy sustain, life steal, and safety.
Improved attacks and sustained damage
Attacking and moving builds energy stacks. At 100 stacks, your next attack heals you and grants increased MS.
Excess healing on you becomes a shield.
Takedowns on enemies grant permanent Lifesteal.
Deal more damage to champion with more maximum health than you.
9% attack speed, 10 ability power or 6 attack damage
Recover health when you damage an enemy champion.
After killing an enemy ward, a friendly Zombie Ward is raised in its place.
Fleet Footwork is a great AD Carry keystone for champions who can be abused by their short range, allowing them to sustain reliably into the late game.
Overheal synergizes well with Fleet Footwork, Bloodline, and Taste of Blood, keeping to topped off in lane.
The Life Steal from Bloodline in the late game is incredibly strong on Sivir with her heavy Crit stacking.
Cut Down is great for chopping down tanks, melee supports, and mid laners who might build Rylais and/or Liandries.
With the bounce from [W], Sivir can easily proc the heal from taste of Blood without even trying to hit the enemy champions, allowing you to sustain in lane.
Zombie Ward is a great rune for lane safety vision, especially placing trinket wards in the tri-brush where they may not be cleared for a while.