There are 3 different arenas - Crystal Crown League, Trial Of The Champion, Free Team-up Arena. With all arenas, when you choose an opponent to battle, you will be shown 3 different opponents. The first two tend to be more difficult with a higher ranking whilst the 3rd one is easier with a lower ranking but will get you less points.
Crystal Crown League
In this arena, you battle with 6 heroes with the usual formation (2 front, 4 back). The first 2 battles in these arena are free but after that each battle costs one Arena Ticket.
You can also set the defensive lineup though this can be different to the lineup that you attack with.
Trial Of The Champion
In this arena, you battle with 3 sets of 6 heroes. When battling, the first set from each team will fight, followed by the second set from each team and if it's still a tie, the third set will fight.
The battles in this arena cost 2 Arena Tickets.
When you battle, you can choose what order your sets are in
You can also set the defensive lineup though this can be different to the lineup that you attack with
Free Team-up Arena
In this arena, you team up with 2 other players. Each player will provide a 6 hero team to fight with. Once you have entered with 2 other players, you cannot change your player team, but you can still edit your hero line up.
Once a player team is formed, only the team leader (whichever player created the team) can do battles, meaning that if you're not the team leader, you can pretty much sit back and relax.
Battles cost stamina. When the team is formed, you get 6 stamina to start with and 1 is generated ever 2hrs to a maximum of 12.
The team leader can arrange what order the sets will be in before going into the Battle list. Rearranging this order affects both the offensive and defensive lineup. You cannot choose what order your sets are in without going out of the Battle list which means it's a little harder to arrange your team against a specific player (as the list refreshes whenever you load it)
When battling, the first set from each team will fight, followed by the second set from each team and if it's still a tie, the third set will fight.