Ok, let's start with its moveset. It has 3 Fire Type moves which is not recommended. Fire Pledge may be a good move on other Fire Type Pokemon, but not Cinderace. With 65 Sp. A, Fire Pledge will barely do anything. Using Physical moves with a 116 attack is a lot better. I will put a moveset and recommended items for Cinderace down below. Now, in-game, Cinderace is a great Pokemon to use and in-game, and this moveset is recommended:
Cinderace @Life Orb (To maximize its potential to OHKO)
Ability: Libero/Blaze (If you have Libero, then Libero. Don't have Libero, then Blaze)
Pyro Ball (Its devastatingly powerful Signature move)
Revenge/Low Sweep/Low Kick (Description under moveset)
U-turn/Blaze Kick (Description under moveset)
Iron Head (To deal with its weakness to Rock, good power)
So Revenge is not the best choice because Cinderace has a great 119 Speed but Revenge is -4 priority, making it likely to move last. However, it may double power if your opponent attacks you. Low Sweep is for the Rock Gym, which Gordie has many heavy Pokemon, thus making Low Sweep powerful. Low Kick is to lower the speed of fast threats and has decent power. U-turn is for pivoting, while Blaze Kick is for when you run out of Pyro Balls.
Now, lets move on to competitively. Cinderace is also a good Pokemon in competitive, being put in the Ubers tier after the release of its Hidden Ability, Libero. A good item to use is Life Orb, raising its attack. However, Life Orb takes away 10% of your health every turn, which is not good. Another good choice competitively is Heavy-Duty Boots. It prevents it from getting poisoned from Toxic Spikes and taking damage from Stealth Rocks and Spikes. Here is the competitive moveset:
Cinderace @Heavy Duty Boots/Life Orb/Choice Band
Pyro Ball (STAB fire move)
High Jump Kick (Powerful fighting coverage)
Iron Head (Good Rock coverage)
U-turn/Court change (U-turn for pivoting, Court Change to get set up like Reflect and Spikes working to your advantage.)
Hope I helped!