During Paul's battle with Ash in the Lily of the Valley Conference it was revealed that Lairon had evolved. Aggron battled against Ash's Pikachu and gained the advantage before Pikachu was switched out and replaced by Infernape. Aggron used Double-Edge while Infernape countered with Flare Blitz. Due to its Rock Head ability, Aggron was immune to Double-Edge's recoil effect. However Infernape's Flare Blitz was been strong enough to burn Aggron and when Aggron attempted to use Flash Cannon, Infernape hit it with Mach Punch before it could launch the attack, knocking it unconscious.
In my opinion, Aggron is 1/3 of the weakest Pokemon with Paul's Nidoking and Hariyama.