ArenaIn Arena, you can host or join in the user-generated battle.

After filling in the battle type, Arena type, and regulation, you can create your original Arena. When Arena is "Public," you can join in the Arena.

In the arena, there are both hosting limits and participation limits. Normally, you can participate in and host up to 3 arenas at the same time, but with Prime, you can participate in and host up to 10 arenas simultaneously.

You can see some events with rewards by the other users, and it's better to check frequently.