Lane bully, skirmishing, and front-line tankiness.
Durability and crowd control
After immobilizing an enemy champion gain defenses and later deal a burst of adaptive damage around you.
After taking damage from an enemy champion, the next 3 spells or attacks you receive deal less damage.
Gain 5 Magic Resist. Whenever you heal for at least 20 health or from a consumable's effect, increase your Magic Resist by 5% for 3 seconds.
Every 8 monsters or enemy minions that die near you permanently increases your max health by 0.2%.
+65 health and +10 AP or 6 AD, adaptive
Periodically your next ability used has its mana or energy cost refunded and restores some of your missing mana or energy.
Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
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
Bone Plating's early game damage mitigation allows you to take early aggressive trades and come out ahead. Your [W] taunt forces the opponent to take the fight and not wait out the duration.
Galio loves Magic Resist for both offense and defense. Mirror shell gives you some early MR and further helps your MR scale into the late game.
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.
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.
Entering the mid-game, Multiple successful taunts from [W] will make or break your teamfights and CDR is what enables that.