Lane utility, reliable damage, and front-line tanking.
Creative tools and rule bending
Your first attack against an enemy champion slows them (per unit cooldown). Slowing champions with active items shoots a freeze ray at them, creating a lingering slow zone.
You get free boots at 10 min. but you cannot buy boots before then. These boots give additional MS. For each takedown you acquire the boots 30s sooner.
Get a free biscuit every 3 minutes, until 12 minutes. Biscuits heal and permanently increase your max mana.
Bonus MS towards nearby allies that are movement impaired or enemies that you impair movement on.
Durability and crowd control
After 10 minutes gain 8 Armor and 8 Magic Resist and increase your total Armor and Magic Resist by 5%.
Gain permanent health when enemy minions or monsters die near you.
+5 Armor or 6 MR (match-up)
Glacial Augment's slow is great for setting up a well-charged Q or follow-up damage while in passive form after dying.
Magical Footwear's raw gold value accelerates your tank items in the mid game so that you become an unkillable machine,.
Biscuit Delivery's missing health regen synergizes well with Sion's large health pool for massive sustain lane pressure.
The extra movement speed from Approach Velocity is great when paired with Glacial Augment, allowing you to chase and stick to targets slowed from autos, [Q], and [E].
Conditioning is an incredibly strong scaling rune that can make you a late game monster tank, but if you're playing into a strong early laner take Iron Skin or Mirror Shell instead.
Overgrowth synergizes incredibly well with Sion's [W] passive allowing you to hit massive health number in the mid to late game.