Battle Arena

Battle Arena is a mode in Bloons TD Battles Mobile that was soft-released for Android on August 19, 2015 and fully released for iOS on August 25, 2015. It involves three different leagues, and the player can enter any. They cost medallions, and each league has a different medallion cost. At the tower selection screen, your medallions along with your opponent's are then placed in a trophy and a map is picked. There is different rules in an arena (including but not limited to Free Boosts, Classic, etc.). You then battle with that rule chosen. Whoever wins the battle will take all the medallions. You can rematch if you'd like, but your opponent must accept. If you rematch, then your medallions are taken to the trophy and the same rules follows.

Your medallions you earned are placed in a Weekly Leaderboard (take note rematches does not count). You qualify for it once you win 100 medallions. Staying in a certain position can win you medallions at the end of that week. Afterwards, the Weekly Leaderboards are then reset.

Leagues
There are different types of leagues, all costing differently. Be aware that if you go on a higher rank, you will be taking risk of your medallions if you lose.
 * Yellow Stadium: Costs 5. A basic league that is used if you plan not to lose too many medallions. If you win, you will earn back your medallions PLUS your opponent's, giving you 10 and making your opponent losing 5. It is the opposite if you lose the battle.
 * White Wasteland: Costs 20. An intermediate league that is used normally. If you win, you earn 40.
 * Lead Dungeon: Costs 100. This league is used if you want to win tons of medallions. Take note that this is very risky, and if you lose, you risk losing 100. Fortunally, if you win, you win a whopping 200. If you want to earn the COBRA more safely, use this league.
 * Rainbow Ruins: Cost 500. Also commonly used to get the COBRA more faster. If you win, 1000 are added to your bank, but be careful as 500 medallions are not easy to collect.
 * Ceramic Crucible: Cost 2000. This is a very high rank of the leagues and winning a battle gives you 4000. Similar to Rainbow Ruins, you will be taking risk if you enter as if you lose, you lose 2000 hard-to-get medallions.

Trivia

 * All the leagues are based off of the bloon types.