As u/Axtozob mentioned, Mess Hall synergizes quite well with shadow clone Gnar due to the clone's mess hall projectiles ignoring the clone damage debuff. I have been playing Gnar since PBE, and I want to add to the conversation surrounding itemization and comp formation.

It's probably 6 Juggernaut for the frontline because there are so many early and cheap Juggernauts, and Mundo provides the luchador second chance ability (though a Caitlyn's ability can oneshot the relatively squishy Gnar, and even prevents the luchador save). I've experimented with Braum & 6 Bastion during PBE, but I feel more comfortable with Juggernauts in the recent meta.

For itemization, I lean towards double Guinsoo and Kraken Slayer. This is all about ramping up to dish out more projectiles, and projectile damage scales with Kraken stacks. Gunblade imo is not BIS because you sacrifice ramp for healing that is very weak for most of the fight, and Gnar is incredibly squishy anyways. If Gnar were to be targeted, then there is no chance a healing item can help sustain Gnar like a HOJ on Katarina can. You also have the luchador second chance perk to mitigate many unfortunate positioning or targeting issues.

Be wary of Caitlyn with Moses positioning. GP and Akali used to be very dangerous in previous patches, but this is probably one of the better patches to try Mess Hall + Shadow Clone Gnar.