Gnar excels by utilizing Mini Gnar's strong poke and mobility in lane, then dominating teamfights with Mega Gnar's tankiness and area-of-effect crowd control.
He is exceptionally strong against melee bruisers, creating a frustrating lane experience with his stun, slow, and movement speed buffs, often warranting a ban.
Consider countering with Comet Malphite or Wukong (post-level 6); understanding his transformation is key to exploiting Mini Gnar's vulnerability or evading Mega Gnar's potent CC.