From Bulbapedia, the community-driven Pokémon encyclopedia.
The Hearthome City Tag Battle Competition is the tournament that Ash, Brock and Dawn took part in Tag! We're It!, Glory Blaze, and Smells Like Team Spirit. It is hosted by Enta. The prize is two Soothe Bells, one for each winner.
The tournament pairs up two different people, using a battle card with presumably two numbers, that person and their partner. The Double Battles take place one at a time in a giant stadium. 32 Trainers are allowed to enter, together forming 16 teams.
Pokémon used in competition
After Paul released Chimchar in Glory Blaze, it joined Ash's team and was used in the final battle.
Pokémon used by other Trainers