I've noticed there are a lot of battles raging over Sion's AP kit, with high regards to his hybrid strategy Death's Caress. I think a fresh full-AD kit is in order, and just like Master Yi, it shouldn't impact the fan base too much. New spell names included...now enjoy :D

Rusted Steel: Sion's basic attacks apply a DoT of magic damage over 3s that can stack up to 3 times. Sion can heal for a small amount per basic attack on marked enemies, the value of which does not stack.
DoT 15/21/27/33/39 (+10% Bonus AD)
Heal 6/10/14/18/22 (+6% Bonus AD)

Enrage: Sion becomes enraged for 7s, increasing his total AD by a small percentage for the duration. Sion permanently gains a small amount of HP per unit slain, the value doubled while the active portion is in effect.
AD Bonus 8/10/12/14/16%
HP Bonus 2/3/4/5/6
Mana 55/65/75/85/95
Cooldown 16

Death's Caress: Sion focuses his power, gaining an HP shield that lasts up to 5s. If the shield remains intact for the full 5s, it detonates to inflict magic damage on surrounding enemies and Stun them for 1.5s.
Shield/Damage 50/105/160/215/270 (120% Bonus AD)
Mana 80/90/100/110/120
Cooldown 11

Cannibalize: Sion reaches peak bloodlust, receiving bonus Lifesteal and Attack Speed for the next 15s. Allies near Sion's basic attack target are healed for a fixed 40% of damage.
Lifesteal 40/55/70%
Attack Speed 35/50/65%
Mana 125
Cooldown 110/105/90

Ability "Dulled Nerves": Sion resists 7/8/9/10/11% physical damage and 10/11/12/13/14% magic damage. This value increases at Level 4/8/12/16.