How do you level up pupitar fast?

To level up Pupitar quickly, focus on battling high-experience Pokémon in areas like caves or the Elite Four if available in your game. Utilize experience-boosting items like Exp. Share to ensure it gains experience even when not in battle. Additionally, participating in raids or using rare candies can effectively increase its level. Lastly, consider using a Pokémon with a type advantage to maximize battle efficiency.