Ranged matchups: Lane sustain and diving tankiness.
Durability and crowd control
Every 4s your next attack on a champion deals bonus damage, heals you, and permanently increases your health.
Charge up a powerful attack against a tower while near it.
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.
Empowered abilities and resource manipulation
Hitting enemy champions with a spell grants maximum mana.
After reaching 250 mana, Manaflow Band restores 1% of your missing mana every 5 seconds.
Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
+6 Armor or 8 MR (match-up)
Ornn is often trading in lane with Brittle empowered auto-attacks, making Grasp a great choice for additional damage and sustain.
Demolish on Ornn synergizes well with you health-heavy item build to ensure you punish successful teamfight victories with tower gold.
Conditioning's double bonus resists synergizes well with Orn''s [E] damage as well as role as a front-line tank.
Oppressive lanes: If you're playing into an incredibly oppressive lane (Teemo) Second Wind here will help you survive lane a lot more safely.
Overgrowth synergizes well with your tanky health build and passive resists, making you incredibly difficult to take down.
Manaflow Band grants you the mana sustain you need to stay in lane as long as possible so that you're able to effectively use your passive and abuse item power-spikes.
Transcendence's mid-game CDR is massively powerful on a teamfight orientend champion such as Ornn. The extra CDR means more CC, more shielding, and more damage.