Battle Arena (BTDB1)

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. The cost is free if the player decides to watch an ad. A basic league for players starting out or players who don't want to lose their medallions. More advanced players will generally avoid this low arena as newer players are a majority, making for less interesting games. Like any arena, a win will give you all the medallions spent to get in, giving you 10 (But you will only profit 5 because you spent 5 to get in) and making your opponent lose 5. It is the opposite if you lose the battle. This arena awards no keys.
 * 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. A beginner league for those who stepped up from Yellow Stadium. If you win, you earn 40 (But you will only profit 20 because you spent 20 to get in). This arena awards no keys.
 * Winter Wonderland: Another replacement for the regular White Wasteland arena on December 14, 2015. It costs the same as White Wasteland, but rewards 50 a victory.
 * Lead Dungeon: Costs 100. If you win, you earn 200 (But you will only profit 100 because you spent 100 to get in). If you want to earn the COBRA more safely, use this league. This arena awards 1 key.
 * Rainbow Ruins: Cost 500. Also commonly used to get the COBRA faster. If you win, 1,000 are added to your bank (But you will only profit 500 because you spent 500 to get in). This arena awards 10 keys.
 * Ceramic Crucible: Cost 2,000. For most of the week, this is the arena with the highest earnings at 4,000 (But you will only profit 2,000 because you spent 2,000 to get in) so expect to face experienced players. This arena awards 40 keys.
 * 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 (But you will only profit 10,000 because you spent 10,000 to get in) bounty, players will need to master their strategies to succeed. This arena awards 200 keys.
 * 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.
 * After update 6.10, bonus 4th tower in MOAB Pit and higher arenas is no longer an option. This makes the games more fair by reducing the random aspect.
 * 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 (But you will only profit 25,000 because you spent 25,000 to get in). This arena awards 500 keys.
 * Boss arenas (Bloonarius Swamp, Vortex Storm, Blastapopoulos Inferno, and Dreadbloon Cave) cost 35,000 and a win awards one with 70,000 (But you will only profit 35,000 because you spent 35,000 to get in) . Beware of very smart players and try your best here. These arenas award 850 keys.

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. You also start with 1400 cash and 500 eco. Recommended towers includes Banana Farms, Super Monkeys, or any slow down tower, like Ice Monkey, Ninja Monkey, Mortar Monkey, or Glue Monkey. 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 if you have farms.
 * Random Trio: Both players are given the same random tower and power selection, and no bonus 4th 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. Similarly, if your towers can’t pop lead bloons, be sure to be the first one to send those on round 8. Skipping the map will give 3 different towers but won’t change the powers.
 * Play 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 and farms are avoided. Rubber To Gold is a very popular choice in this arena.
 * Mega Boosts: Tower Boost upgrades all towers on the path with the most upgrades, while Bloon Boost makes all bloons sent upgraded by one layer for 10 seconds. Tower boosting multiple towers at once is a common tactic and saves money with expensive upgrades, like Banana Research Facilities or Sun Temple. When you use a Tower Boost while having multiple Sun Avatars, they all become temples, regardless of their placement on the map. If you refuse the sacrifice, your Tower Boost is still spent and upgrades other towers. On the other hand, 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 (red bloons and spaced blue bloons can be sent right when the game starts, during the pre-game) and players' income generates every 4.3 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. The health ramping starting from round 30 also increases significantly faster, which, combined with the speed stance, makes for some very deadly moabs very quickly.

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. Rewards are always equal to two times the cost of attempting this arena. Costs 35,000.
 * Vortex Storm. Rewards are always equal to two times the cost of attempting this arena. Costs 35,000.
 * Dreadbloon Cave. Rewards are always equal to two times the cost of attempting this arena. Usually costs 35,000, and had formerly costed 50,000 in the past.
 * Blastapopoluos Inferno. Rewards are always equal to two times the cost of attempting this arena. Usually costs 35,000, and had formerly costed 500,000 in the past.

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 good 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, White Wasteland is good, since it is a low-stakes arena. Higher-stakes arenas are not a good idea until you have plenty of skill.
 * It is not advised to play on Yellow Stadium, as you get 5-7 (and can't lose) from playing normal Assualt or Defense. There is only one advantage of playing Yellow Stadium compared to Classic Battle, which is to use free bonus towers, free boosts, and free Red Hot Spikes for every game, which is useful when Battle Energy is low.
 * 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 (formally), 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.
 * The Blastapopoulos Inferno has a little pond of water in what used to be part lava, of which lava is unplaceable land.
 * Compared to Yellow Stadium, Assault Mode does not have a possibility of losing medallions during defeat, but instead gives a consolation of 2. However, Yellow Stadium allows fourth towers to be accessible at no cost at all.
 * Arenas will actually add to your leaderboard score double the amount you paid when you win. This is because the fee you used to enter is not counted (in fact all fees are not counted) and adds only the prize. Prestige leaderboards, however, will count both fees and prizes, so you only get the score you paid in medallions when you win, and decreases when you lose.