Hello i am pioj12, i'm a gnar main and thought that making a gnar guide for new players interested in gnar will be fun, All this guide is based on my almost 300-500 matches as gnar experiences hope you enjoy it and leave a like if you want :D

Pros:
-Good oneshot potential
-Hybrid character
-Very safe on lane
-Cute
-Easy to climb

So this is quite simple, as mini gnar try to poke a lot of the enemy and get stacks on Grasp of the Undying, after you get lvl 2 you have to options, you can go for an all in lvl 2 bc you are going to have your Rage Gene up or try to hold your Rage Gene to get lvl 3 to all in.
There are not that many matchups That you lose as Mega Gnar at lvl 2/3 so you can start snowballing from there.
An essential part of gnar is freezing the wave bc you can all in whenever you want as mega and easily poke the enemy from the safety of your tower with basic attacks and you Boomerang Throw.
Try to all in your enemy when you are mega to get a good trade and even kill or force him back.
Some of this playstyle/rules are broken into really hard matchups.

A little trick that not much gnar mains do is that you can Hop of an enemy minions to transform mid air into Mega Gnar, you can also Hop from allies into a team fight to gap close into the enemy to get a good GNAR!, or in laning phase you can spam a unexpected Wallop to land a ez stun on the enemy.
You can also use GNAR! in mid air!! Play Video Always try to destroy the tower so you can rotate and use your presence in teamfights.
Always try to positionate in a team fight to get a good GNAR!, some good ults can even pick off 3 people or win an already lost teamfight.
A thing that many gnars players don't know is that it is ez to dive into a turret (As Mega Gnar) so try practicing that.

There's always a choice to make while playing gnar and this is the mythic item to choose the options most of the time are Iceborn Gauntlet and Stridebreaker. Each item offers you something different but in my personal opinion I prefer the Iceborn Gauntlet for the stats and active but let's take a look and when you should buy each item shall we?
This depends on the next factors
- Iceborn Gauntlet, you will use this item when you are the only tank and the enemy has a lot of mixed damage.
- Stridebreaker, You will be using this item when you have a good main tank (usually from the jg) and want a little bit more cc.
For the resto fo the items are usually match dependant but you will usually build the core items and then take more tanky items bc you are going to be usually the main tank of the team.

So there's only two rune pages that i consider good for laning phase that are the Grasp of the Undying and Fleet Footwork each has his advantages and the Blade of the Ruined King is more of a fun rune page so lets cover each one.
GRASP RUNE PAGE:
So first of all lets cover the main rune being Grasp of the Undying this rune is usually very ez to pop into an enemy toplaner bc you are a ranged top laner so in must matches you can grab a lot of stacks.
We bring Demolish bc gnar is good split pushing and also as a team fighter so most of the time you need to be with your team and to do that and make early plays you need to destroy the enemy tower and when needed split to destroy more towers.
We also bring Bone Plating and Overgrowth to help us scale a little bit and take less damage.
The secondary runes are just for sustain in lane.
Fleet Footwork runes.
When normally use Fleet Footwork into ranged vs ranged matchup in top lane bc it gives us a lot of sustain for trades and keeps us healthy for all in as Megas Form.
We also bring Triumph, Legend: Alacrity and Coup de Grace to help our 1v1 on lane.
The secondary runes are for the same purpose as above to have split push potential and take less damage.
Blade of the ruined king runes.
This runes are the same as fleet but changing the keystone from Fleet Footwork to Press the Attack, the main idea of this rune page is to make a lot of damage as mini gnar and have kitting potential thx for Blade of the Ruined King so as soon as you pop the three basics for Press the Attack you also pop Hyper and the effect of Blade of the Ruined King the build is fun to play but tbh the other normal builds are better since you kinda lose a key rune and need to build damage items such as Black Cleaver to not lose damage.

Overall gnar is a pretty good top laner and a safe pick has split push potential thx to Demolish and teamfight only downsides could be the "bad timing" on his passive but at the same it offers all in/poke potential.
Hope you liked my guide. I will happily make a discussion in the comments to improve this guide, and I will keep it updated.
Have fun playing gnar :D.