Gnar is just a fun little guy to play!

But in all seriousness, his ability to tank damage as well as deal it is fantastic in the bot lane. You are free to play him safely while waiting for mega form and then engage with lots of burst during lane or later in the game.

As far as I'm personally concerned, Arcane Comet is going to be the best rune for Gnar support. Its super easy to proc and land thanks to Gnar's Q Boomerang Throw. Nimbus Cloak is 99% of the time going to be better than Nullifying Orb unless youre versus Ziggs adc or something of the sort. Transcendence is just good in general for the CDR bonus. Finally for the main keystone route, Scorch is just a nice bit of added poke for Gnar, and since youre not going damage, Gathering Storm isnt very worth it in the end.

In the Resolve tree I like taking Second Wind because it feels a little better than Bone Plating if you constantly want to trade and use your Arcane Comet in lane. Overgrowth is more of a bonus in the end for mega gnar since youre relying on the gained tank stats to help you dive into the backline. You can argue for Unflinching but I would not recommend it if youre not into mass amounts of CC.

Steel Shoulderguards will always be the best choice of a starting item. Choosing Spectral Sickle forces you to rely on landing autos and Boomerang Throws which could lead to early deaths or lost trades. On top of that, the added 25% health regen is way better than the unneeded mana regen for Gnar's nonexistent mana pool.

Moving on to the mythic of choice, you're going to want to go with Locket of the Iron Solari. The tank stats provided are great and its awesome for the budget support Gnar is given. As Gnar support youre more focused on being a team player and setting up for your teams success, so why not also give them a shield and bonus armor and magic resist as well! Another option not listed is Turbo Chemtank, though this is almost selfish and more expensive for the support budget we're working with.