I'll start off by saying, I love Ornn. He definitely keeps with your promise of thinking outside of the box for new champ abilities.
I have only one suggestion. Ornn is a blacksmith, and even he proclaims he loves his hammer. Why not give him one? One of his master craft items should be the Frozen Mallet. Give it +20 damage and +200 health. He focuses on health and CC. The mallet plays to both of those. Seems like a given to me.
Dehydration1 votesI think he already has enough item upgrades and on the items that everyone would have at least 1 of.
Embermoore1 votesYou're right. Perhaps the hammer would be something that only he could have.
LostFr0st1 votesHis hammer is the precious though, he wouldn't think it needs upgrading...
ThorOdinson541 votesBut it's the FROZEN mallet, and he's the FIRE under the mountain...
Really though, the Frozen Mallet seems like a strong enough item for him without extra buffs.