There are three types of battle (player versus player) combat modes currently available in the game.
The Phantom Battle arena is an automated combat of your 3 character team against another player’s 3 character team- you can choose which team you go up against. You can also choose to skip the animation of the combat once it loads and it will just tell you who won or lost.
You should do the arena 5 times a day for the rewards such as coins for the arena shop and potential gem rewards. You must be level 30 to access the arena.
There are two forms of live PvP (player vs player) match- ranked match and friend match. You must be player level 85 to enter PvP.
Ranked matches are only available occasionally for a week long period, whereas friend matches are permanently available.
Draft match allows you to have turn based battles with selected units against other players. You must be level 20 to access Draft Match. Draft match is only available occasionally for a week long period.