NOTE these are only my initial thoughts on Gnar after a few games with him on PBE some of these can very quickly change once I get off PBE and play against players of a better skill level on live servers.

Champion:


Gnar is a an interesting adapting champion that morphs between ranged and melle forms throughout the game. Unlike the other "morphing" champions who can morph at will as their ultimate Gnar's morph is related to his passive and his resource bar. Gnar starts the game as a "Mini" Gnar form. In this form Gnar plays as a mobile kite champion who uses poke slows speed boosts and percent health damage to deal with his opponents. This form is safe most of the time in lane and unless you get all in'd by an assassin or get ganked and waste your escape move and will allow you to play safe farm and poke the enemy laner. The area Gnar mainly lacks is a direct form of sustain, meaning lifesteal will be very important in any lane where the enemy has a reliable form of poke they can use against you. Once you reach 100% on your resource bar you begin a whole different game "Mega" Gnar. As Mega Gnar you are given a truckload of free defensive stats in exchange for becoming a slower (easily Kitable) melee champion. In this form you are given a truckload of CC and bonus damage until your bar empties out. The main thing to look out for while playing Gnar is keeping track of your resource bar. The best thing I can relate him to as a champion is a Nidalee/Jayce style champion with rotating ranges with a rumble style of resource. Flipping from a poke style of play to an all in style of play as the game goes on will be important to be a good Gnar.

Skills(Most of these are current numbers from the Gnar Wiki page):



Rage Gene- At maximum Fury Gnar's next ability will cause him to transform, granting him access to an alternate set of abilities for 15 seconds while his Fury depletes. After ~5 seconds, Gnar will transform automatically. Once his Fury is exhausted, Gnar will return to normal and cannot gain Fury again for ~15 seconds.
Gnar gains different bonuses based on his current form:
Mini Gnar:
Movement speed: 10 - 18 / 20 - 38
Attack range: 244 + (6 × Gnar's level)
Attack speed: (5 × Gnar's level) %
Mega Gnar:
Health: 30 + (40 × Gnar's level)
Armor / Magic resist: (2 × Gnar's level)
Health regen: (3 × Gnar's level)
Base Attack damage: 4 + (2 × Gnar's level)

Alot of numbers but it is mainly just the stat changes he gets for morphing between his forms. The big thing to notice is that your auto attack range scales up with your level so its like a tristana in that your range in lane will not be what your range mid-lategame is. The other big thing to note is the HP he gets by morphing into mega form. This hp scales up to about 700~ endgame and GIVES you the health when your morph meaning when the morph ends you keep the health you gained from the transformation turning this into an artificial form of sustain.




MINI GNAR - ACTIVE: Gnar throws his boomerang forward in a line, dealing 10 / 45 / 80 / 115 / 150 (+ 100% AD) physical damage and slowings movement speed by 15 / 20 / 25 / 30 / 35% for 2 seconds before returning towards him. The boomerang then returns to Gnar, dealing 50% of the initial damage to all enemies it passes through. If Gnar catches his boomerang, Boomerang Throw's cooldown is reduced by 60%. RANGE: 1100 COOLDOWN: 20 / 17.5 / 15 / 12.5 / 10.

This move will be one of your main forms of harass in lane and will also help you push the wave. The best way I can think of this move is as what Draven's spinning axe was designed to be like. When you throw the boomerang it will do damage then start coming back towards you. If you catch the boomerang you get a massive CD reduction on it (at max rank it pretty much is auto refreshed). If you miss this move yo have to wait the full cooldown which in a fight could mean life or death. The slow from this move is very useful for chasing/kiting enemies. Just remember once the boomerang hits a target it will only go a little bit more distance forward before it will turn back around and come towards the direction you are in.



MEGA GNAR - ACTIVE: Gnar throws a boulder that stops when it hits an enemy, dealing 10 / 50 / 90 / 130 / 170 (+ 120% AD) physical damage and slowing all enemies hit within X-range by 15 / 20 / 25 / 30 / 35%. If Gnar picks up his boulder, Boulder Toss's cooldown is reduced by 60%. RANGE: 1100 COOLDOWN: 20 / 17.5 / 15 / 12.5 / 10.

Pretty much the same concept as mini Gnar's boomerang xcept that it does more damage and is like an Olaf Undertow where you have to go pick it up where you threw it to. It is decent for poking while in mega form as well as well as dealing a good amount of AoE damage when you are in the enemy team.



MINI GNAR Hyper - PASSIVE: Every 3rd consecutive attack or spell on the same target grants Gnar 30% bonus movement speed that decays over 3 seconds, and deals additional magic damage equal to a base amount plus a percentage of the target's max health [25 / 30 / 35 / 40 / 45 (+ 100% AP) (+ 6 / 8 / 10 / 12 / 14% of target's max. health)] (Capped against minions and monsters at 70 / 125 / 175 / 225 / 275). Gnar gains Hyper's bonus movement speed whenever he returned to Mini Gnar from Mega Gnar.

This passive gives Gnar the ability to kite targets as well as the ability to wear down tanky targets. Think of this as a magical silver bolts that gives a MS boost when procd. This also makes it hard for enemies to build one type of defensive stat against Gnar, making him hard to counterbuild. Note that your Q and E also will put marks on the target so one auto with both your skills will proc the passive incase you need movespeed.



MEGA GNAR Wallop - ACTIVE: Gnar stands on his back legs before slamming his fists into the ground, dealing 25 / 50 / 75 / 100 / 125 (+ 100% AD) physical damage and stunning enemies in a large area in front of him for 1.25 seconds. 12 / 11 / 10 / 9 / 8

Just some more CC to set up mega form stuff. Damage and a stun.




MINI GNAR Hop - ACTIVE: Gnar leaps to a location, gaining bonus 20 / 30 / 40 / 50 / 60% attack speed for 3 seconds. If Gnar lands on a unit he will bounce off it, traveling further, dealing 20 / 60 / 100 / 140 / 180 (+ 6% of Gnar's max. health) physical damage and briefly slowing the unit landed on if was an enemy. RANGE: 475 COOLDOWN: 18 / 16.5 / 15 / 13.5 / 12.

This move is gnar's main escape and positioning tool. Its damage is based on Gnar's health meaning that building hp will scale into damage on Gnar. Jumping on any creep, jungle monster, or champion will cause you to jump forward in the same direction you jumped towards in order to hit them. If you use this move at 100 fury you will double jump as the Mega form.


MEGA GNAR Crunch - ACTIVE: Gnar leaps to a location, dealing 20 / 60 / 100 / 140 / 180 (+ 6% of Gnar's max. health) physical damage to all nearby enemies on landing, enemies on the center of the impact area are slowed briefly. COOLDOWN: 18 / 16.5 / 15 / 13.5 / 12

This move is just like the mini forms jump except you get a slow for landing on an enemy target instead of a double bounce. This is a trade of mobility for CC which will allow you to stick to an enemy for a little while in mega form if you are able to hit the jump.


GNAR!- MINI GNAR - PASSIVE: Hyper's movement speed bonus is increased to 45 / 60 / 75%.
MEGA GNAR - ACTIVE: Gnar knocks all nearby enemies in the specified direction, dealing 200 / 300 / 400 (+ 50% Bonus AD) physical damage and slowing them by 60% for a short duration (1.5 / 1.75 / 2 seconds). Any enemy that hits terrain takes 50% increased damage 100 / 150 / 200 (+ 25% Bonus AD) and are stunned instead of slowed. RANGE: 590 COOLDOWN: 120 / 100 / 80

The ultimate increases the movement speed you gain from your passive in mini form allowing you to kite better as the game goes on. In your mega form you get access to the actual ultimate a thresh flay that will stun enemies who get rammed into terrain. This ability is really useful for CC and positioning purposes and can make fighting Gnar near a wall dangerous.

Itemization:


Itemization for Gnar is tricky because you have to keep both of his forms in mind. So far the main items I see being useful on him are:

Tier 1:
Blade of the Ruined King- Adds kiting potential and chasing potential in mega form.
Youmuu's Ghostblade- The item has a generally good synergy with Gnar.

Tier 2:
Warmog's Armor-Bonus defensive stats in Mega form scale well with H
Trinity Force- Popping trinity force in between human form Qs adds a decent amount of damage.
Black Cleaver-CDR, Hp, and helps your allies do more damage.

I haven't thought into much else. If anyone wants to add build ideas they can throw them in the comments.

Skill Requirements IMO (What makes a good Gnar):


The main points I think will make a good Gnar:

-Keeping Track of passive
-Catching all the Qs.
-Kiting with a lower range.
-Knowing where you will hop and landing your hops so that they get you where you need to be.
-Managing form shifts as a form of sustain.
-Landing as big of a stun possible with your ultimate
-Spamming emotes whenever you get the chance.

Conclusion:


Thats all I have to write on my first thoughts of Gnar as a top laner as PBE cycles come he may change, Ill get to try him out more in the coming days experiment with some more builds and think of other fun things to do with him. As always summoners have a good day and good luck on the fields of justice!