Abilities of Sion
Spell skill priority is an important winning factor for Sion. Understanding the abilities of Sion in League of Legends is another. Below you can find all the relevant information on Sion abilities. In order for item builds you should check the build for Sion.
Passive: Glory in Death
After being killed, Sion will temporarily reanimate with rapidly decaying Health. His attacks become very rapid, heal him, and deal bonus damage based on his target's maximum Health.
Decimating Smash
Sion charges a powerful swing in an area in front of himself that will deal damage to enemies when released. If he charges for enough time, enemies hit by the swing will also be knocked up and stunned.
mindamagetotal and maxdamagetotal physical damage based on charge time. If Sion charged for at least 1 second, enemies are Knocked Up and Stunned for between basestuntime and 2.25 seconds based on charge time.
Soul Furnace
Sion shields himself and can reactivate after 3 seconds to deal Magic Damage to enemies nearby. When Sion kills enemies, he passively gains maximum Health.
Passive: Sion gains hpperkill max Healthhpperchampkill for champion takedowns, large minions and large monsters.
Active: Sion gains totalshield Shield for 6 seconds. After e7 seconds if the shield still holds, Sion can Recast to detonate the shield to deal totaldamage plus e4% max Health magic damage.
Roar of the Slayer
Sion fires a short range shockwave that damages and slows and reduces the Armor of the first enemy hit. If the shockwave hits a minion or monster, it will be knocked back, damaging, slowing, and reducing the Armor of all enemies that it passes through.
Sion fires a shockwave, dealing totaldamage magic damage, Slowing them by slowamount% for slowduration seconds and removing armorshred% Armor for armorshredduration seconds. Non-champions hit are Knocked Back. Enemies hit by a Knocked Back unit take the same damage and effects.
Unstoppable Onslaught
Sion charges in a direction, ramping up speed over time. He can steer his charge slightly with the mouse cursor location. When he collides with an enemy he deals damage and knocks them up based on the distance he has charged.
Sion charges Unstoppably in a direction for 8 seconds, turning towards the mouse cursor. Sion stops on colliding with an enemy champion or wall or on Recasting this Ability.
At the end of the charge, Sion deals between mindamagetotal and maxdamagetotal physical damage based on distance travelled. Enemies close to Sion are Stunned for between minstunduration and maxstunduration seconds based on distance travelled. Enemies in a larger area are Slowed by slowamount% for 3 seconds.
FAQ on Sion
What do you max first on Sion?
Most Sion pros max out 
Decimating Smash first.