gnar is still impossibly strong.
he's the only champion who can pull top damage on his team, all while building 90% tank items. every single smart gnar i've ever seen does the same thing. build extremely tanky, soak damage in 1v1's all while doing a massive 10-14% health magic damage every third attack or ability. and if you do manage to do a lot of damage to him, he pops into mega gnar form to get an even stupider amount of tankiness, a stupid amount of cc(which let's face it, there's walls everywhere so everywhere is a bad position to fight gnar), AND a gap closer. i love playing the little dude, but he's cancer in teamfights and he's cancer in lane too. i have played quite a few games as gnar, and the one most fresh in my memory was a game i had against a yorick. the only damage item i build ALL game, was a hexdrinker(not a maw, just a hexdrinker). the other items were a randuin's banshee's thornmail guardian angel and merc treads. by the end of this 45 minute game, i had 50,000 damage. more than anyone on my team and 2nd most in the game behind the enemy team's adc.
people can say "oh well mini gnar is squishy". he's also damn near impossible to catch, has a short cooldown slow that applies stacks for his passive w that really isn't very hard to catch(the boomerang), and also gets a movespeed bonus on TOP of the 14% health magic damage and when he leaves mega gnar form. and say you do catch up to gnar when he's in mini form. chances are he's landed quite a few hits on you, and once you get him to half health you get slapped with his ult into a wall, followed by a q, followed by a w right after you get out of the first stun, and then when you try to escape he will e in front of you. and say he doesn't kill you right there, the second he leaves mega gnar form, he gets a speed boost which further allows him to chase you down.
tl;dr(seriously couldn't read the whole thing, come on now): Gnar is a toxic champion because he single-handedly carries teamfights, is very hard to itemize against, and is too good at kiting/chasing down.