As a Gnar main with 470K mastery points(and mastery 7), recently Gnar is quite bad in top lane, easily bullied, and susceptible to poke and/or hard engage, with the lethality buffs soon to come, he will be at a even more risk against champions such as Jayce, Wukong, and even Riven.
So what's a Yordle to do? Not only is he weak, but his counters are getting buffed, so how do we counter his weaknesses? By bringing him to a safer environment! Not only is he safer from his enemies, but jungle counters don't matter much. Many would argue that Gnar's ganks are limited to his mega form, and that you'd have a hard time to manage your rage inside the jungle for a gank. Well, I'm here to tell you, it's not impossible, and that mini Gnar is just as dangerous as mega Gnar in a gank, if you can master both, it is best.

1. It's best to pick Gnar if your top laner hasn't chosen yet, and if they won't until later, most enemies will assume Gnar top and pick a counter to Gnar, this gives your top laner a chance to counter pick, since top is counter pick heavy.
2. Another reason to pick Gnar is if their jungler is a tank, Gnar has built in anti tank, and his builds mostly emphasize this.


NOTE:Please have experience, Gnar has difficult mechanics for new players, it's even harder to jungle if you have no clue on how to use Gnar.

1. You'd be the only tank, it could work, but you should at least have someone else be a juggernaut or another fighter, you alone are squishy naturally, pick a dedicated tank if your team needs one.
2. They have someone who could counter your engage and outright kill you, Jayce, Cassiopea, you understand.
3. You're easy to break, by that I mean, if your team gets under your skin before you even play for picking jungle Gnar, then don't play Gnar, period. Gnar top isn't even that good and people won't complain about that, but do something weird and the people go into a blind rage, like adc Ziggs, or support Malzahar.
4. You have no experience with Gnar, or kiting. The hardest thing about this guide is that if you don't know how to manage your rage with the aoe damage from your cinderhulk, or how to kite someone(helps with camps), you won't learn much from the jungle, go top, build sunfire, learn.

Start on the side with the adc always.
Red buff-->raptors-->wolves-->blue-->gromp-->gank/back-->kruggs
Blue buff-->Gromp-->wolves-->red buff-->raptors-->kruggs/gank-->kruggs/back

RAPTORS NOTE: Best way to handle these is with Q, W, and red buff,(can be done without, just be careful) use your auto and throw your Q for an immediate auto cancel, kill the small raptors one by one while weaving your Q's and making them chase you, you take less damage if they're running, pop a potion half way through, and done.

Mini:
Use your Q to gank, it's a slow, but if the enemy is pushed out, it works. If you can get near them and dodge their cc, keep attacking them until they blow their escape, once it's safe, use your smite and keep attacking them, they will eventually blow their flash or you you/your teammate can secure the kill.

Mega:
You only have your E to engage, but avoid ganking a mobile enemy as a mega, unless you can combo stun them long enough for your ally to assist in the kill.

Mini to mega:
Smite then keep autoing them, if possible, throw a Q, if it's safe, jump on the enemy and catch the boomerang mid-air, combo stun.

Mega to mini:
Land a W or a Q and ult even, then smite them and attempt to kill them, or use the movement speed to escape.

The best results I had are:
REDS: Attacks
YELLOWS: Scaling Armor
BLUES: Scaling MR
QUINTS: 3 attacks

The safer route:
REDS: Attacks
YELLOWS: Flat Armor
BLUES: Scaling MR(flats if you want, though I recommend scaling)
Quints: 3 attack speed

When to pick what and why.

Cleaver: recommended, best item for Gnar in terms of stats and utility.

MAW: Recommended, good against ap comps. Do not get if going Sterak's or Death's Dance.

Death's Dance: Buy it if you can afford to burn gold into a lot of attack, usually works best with Spirit Visage, and Maw.

Sterak's Gage: Need a Maw but they don't have strong ap? Get this, works well with Triforce.

Triforce: Get it if you didn't get attack speed runes, or you want to get risky, works well with mini and mega, do not get if you're getting a cleaver, instead, go for Death's Dance if you go cleaver.

Edge of Night: It's an alternative to banshee's veil in terms of damage, the armor pen works well, but it's your call.

Youmoo's: Get if you want to triforce or Edge of Night, works well with both items, the attack speed nerf makes it weaker however.

Iceborn Gauntlet: SPECIFICALLY FOR COUNTERING PURE AD COMPS AND IF YOU DON'T WANT TO GET FROZEN MALLET. This with cleaver works well, and you could just go randuins, tabi, thornmail.