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 is made up of leagues that cost medallions to enter, with higher ranked leagues costing more. At the tower selection screen, your medallions along with your opponent's are then placed in a trophy and a map is picked. There may be different rules in each arena (including but not limited to Free Boosts, Classic, Club Arena, Club Match etc.). You then battle with those rules. Whoever wins the battle will take all the medallions. Rematches can happen, but both players must agree upon it.

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

Leagues

 * Yellow Stadium: Costs 5. You can play for free if the update 3.2 is installed and you watch an ad. A basic league for players starting out or players who don't want to lose their medallions. Like any arena, a win will give you all the medallions spent to get in, giving you 10 and making your opponent lose 5. It is the opposite if you lose the battle.
 * North Pole: A replacement for the regular Yellow Stadium arena on December 14, 2015. It costs the same to enter, but you win 15. Changed back to the Yellow Stadium on TBA date.
 * White Wasteland: Costs 20. An intermediate league that is used normally. If you win, you earn 40.
 * Winter Wonderland: Another replacement for the regular White Wasteland arena on December 14, 2015. It costs the same to enter, but you win 50. Changed back to White Wasteland on TBA date.
 * Lead Dungeon: Costs 100. Winning earns you 200. If you want to earn the COBRA more safely, use this league.
 * Rainbow Ruins: Cost 500. Also commonly used to get the COBRA faster. If you win, 1,000 are added to your bank.
 * Ceramic Crucible: Cost 2,000. For most of the week, this is the arena with the highest earnings at 4,000 so expect to face experienced players.
 * MOAB Pit: Cost 10,000. This is open only during the second to last day in a week in Battle Arena, and lasts 48 hours. With a 20,000 bounty, players will need to master their strategies to succeed.
 * Before update 3.2, MOAB Pit only cost5,000 and winning would earn10,000. It also was open on the last day of the week and lasted 24 hours like BFB Colosseum.
 * BFB Colosseum: Cost 25,000. It is only open during the last day of a week in Battle Arena and lasts 24 hours. If your tactics are sound and you are prepared for everything, winning this Arena earns50,000.

Club Arenas
On update 3.2, Club Battles were open in Battle Arena and Assault Mode. They include special rules including but not limited to random towers being your default towers and other rules. The apply to only a certain number of arenas. Unless you pay $4.99 USD to join the club, you may only play one club game per 24 hours. On update 3.3, Combo Arenas were open and were just two or three of these arenas combined. On update 3.8, Card clubs were introduced with card battles and club rooms combined.


 * Bananza: Every method of cash and economy generation is twice their regular amount, making expensive towers easier to buy. Recommended towers includes Banana Farms, Super Monkeys, Heli-Pilots, or anything powerful. Be ready for late game, as double the cash will make late game more common. Sending MOAB class bloons decreases income by double the normal amount, although this is hardly a problem.
 * Random Trio: Both players are given the same random tower selection, and no bonus tower is allowed. You must be wise with your given towers and rush if you see a weakness. If your towers cannot reliably detect Camo Bloons, kill your opponent on round 12 with boosted camos. Skipping the map will give 3 different towers.
 * Playing With Fire: Bloon economy increasements/decreasements are doubled, but any bloon you send to your opponent is also sent to your side. If you see a weakness in your opponent's defense, don't be afraid to exploit it while ensuring you can survive the rush. Bloon income is usually used in this mode.
 * Mega Boosts: Tower Boost upgrades all towers on the path with the most upgrades, while Bloon Boost temporarily upgrades all Bloons by 1 rank. Tower boosting multiple towers at once is a common tactic and saves money with expensive upgrades, like banana research facilities and super monkey fan clubs. Grouped bloon rushes become especially deadly when Bloon Boosted, so be prepared for them and Tower Boost if necessary.
 * Speed Battles: Bloons moves faster, players can send bloons 2 round earlier (except blue bloons) and players' income generates every 4.5 seconds instead of 6 seconds. Fast bloons can run right through slow attacking towers early on, ensure that your towers can handle them. Notably, BFB's and ZOMG's are extremely fast compared to normal, and most defenses can not handle them easily. The Ninja Monkey and Ice Tower abilities are especially useful in slowing down MOAB class rushes.

Boss Arenas
Added in the 3.5 update, boss arenas are rarer than BFB Colosseum but provide more medallions. They also have a map based on the boss bloon map in Bloons Monkey City.


 * Bloonarius Swamp. Costs may vary. Rewards also vary but are always equal to two times the cost of attempting this arena.
 * Vortex Storm. Costs may vary. Rewards also vary but are always equal to two times the cost of attempting this arena.
 * Dreadbloon Cave. Costs may vary. Rewards also vary but are always equal to two times the cost of attempting this arena.
 * Blastapopoluos Inferno. Costs may vary. Rewards also vary but are always equal to two times the cost of attempting this arena.

Club Challenge
This was also added in the 3.5 update. In this arena, players are given a specific tower loadout, and map choices, and potentially including a Club Arena rule. As the load outs are always identical, playing more matches will give you knowledge of what works with the limitations.

Card Battles
Added in 3.6 update, this arena allows you to use a deck of cards to place towers or send bloons. Your deck may balance on eco bloons, good towers, or aggressor bloons.

This mode is critically rated due to its luck-based environment, and the fact it usually goes late game unless your opponent does not have towers to defend rushes. You can get towers/bloons you expect or get bad towers and easily lose. Thus, it is best to become experienced and flexible with a wide variety of towers and their combinations, not just one specific range, particularly as this type of battle arena involves luck to get a random selection of towers.

Strategies

 * There are some very good players in the Arenas. If you are new to the game or lack strong towers/upgrades, Yellow Stadium is good, since it is a low-stakes arena. Higher-stakes arenas are not a good idea until you have plenty of skill.
 * Remember how many medallions you have. It is possible to lose all of your medallions and have to start back in either the smaller arenas or in Assault Mode.
 * Sending grouped bloons usually causes people with a few towers to use their Tower Boost battle energy to defend. Round 8 and 16 are perfect examples. If you are confident in your abilities, a follow up rush when their battle energy is recharging can lead to an early victory.
 * If it is free power-ups, use them wisely. You and your opponent have only 3 tower and bloon boosts, try to make your opponent waste theirs early on by sending bloons that will cause them to use the tower boost in panic.
 * If it is classic battles, try to stock or save on battle energy as you might need it later.
 * Recommended towers includes Dart Monkey, Ninja Monkey, Banana Farm, COBRA, and others.
 * You aren't the only one reading this guide. Prepare for your opponent having the towers mentioned above.
 * Ranking high in leaderboards will warrant you medallion rewards.

Trivia

 * All the arenas are named after bloons: Yellow, White, Lead, Rainbow, Ceramic, M.O.A.B, B.F.B, Bloonarius, Vortex, Dreadbloon, and Blastapopoulos.
 * There used to be a bug where the player goes to the Mega Boosts Arena or battle and trying to upgrade Sun Gods into Temples via Monkey Boost, making every Temple become sacrificed and disappear after the animation, leading to a very easy defeat or, if still surviving, a waste of cash. It can be seen here. As a result, Super Monkeys should've be best upgraded on path 2 where it can easily be upgraded to Robo Monkey or Technological Terror or be manually upgraded. This is now patched.
 * Boss Bloons are mentioned in the Boss Arenas, even though Boss Bloons do not directly appear in the game yet.