Turn off Mega Gnar
Somehow.
I have used Gnar a few times and find that Mini>Mega- vastly better. Mini has range and speed, and the W passive hyper. 14% of your hp goes down every 3 shots when maxed + my damage. I have pulled stunts on my few ARAM (yes ARAM, I don't own it yet) matches where I knock out 3 people at once before I get triggered into Mega. Then the fun stops. Then I hide in a bush.
Its the same idea as Vayne, though not scaled so strongly. Finding a champ that I build almost NO damage into is amazing. I pull full attack speed Gnar.

=/ I would buy Gnar for keeps IF I could control Mega to Mini morphing in the sense that champs like Nidalee can go from human to cougar at will. =/ Thats all that makes me hate Gnar, otherwise fantastically fun hit and run character.