Galio

Colossal teamfighter

Lane harassment and consistent damage output.

Resolve

Durability and crowd control

Aftershock

After immobilizing an enemy champion gain defenses and later deal a burst of magic damage around you.
Shield Bash

Whenever you gain a shield, your next basic attack against a champion deals bonus adaptive damage.
Conditioning

After 12 min gain +8 Armor and +8 Magic Resist and increase your Armor and Magic Resist by 3%.
Overgrowth

Gain permanent max health when minions or monsters die near you.

Sorcery

Empowered abilities and resource manipulation

Manaflow Band

Hitting an enemy champion with an ability permanently increases your maximum mana by 25, up to 250 mana.

After reaching 250 bonus mana, restore 1% of your missing mana every 5 seconds.
Transcendence

Gain bonuses upon reaching the following levels:
Level 5: +5 Ability Haste
Level 8: +5 Ability Haste
Level 11: On Champion takedown, reduce the remaining cooldown of basic abilities by 20%.

Adaptive Force

+9 Adaptive Force

Why Aftershock

Aftershock is the successor to Courage of the Colossus, but rather than granting a shield it does damage and give a ton of Armor and Magic Resist. Galio loves Magic Resist

Why Shield Bash

Shield Bash synergizes well with Galio's [W] shield, granting a bit of extra resists as well as offensive power.

Why Conditioning

The extra resists from Conditioning empower your ability to absorb a ton of damage in the mid game with [W] and also grant additional damage reduction on your [R].

Why Overgrowth

Overgrowth on Galio makes you a late game monster, empowering your health pool to be a huge frontline tank that dishes out a lot of damage.

WhyManaflow Band

Galio's abilities have relative high mana costs and be needs to spam to keep up with wave pushes. Manaflow Band will give you the needed mana sustain to shove and roam.

WhyTranscendence

Entering the mid-game, Multiple successful taunts from [W] will make or break your teamfights and CDR is what enables that.