Co-Op Mode (BTD5)

 is a new mode added to Bloons TD 5 and Bloons TD 6  in an update that was released on 26th March, 2013 for BTD5 and 2nd July, 2019 for BTD6. It is unlocked at Rank 10 (BTD5) and Level 20 (BTD6). It involves two players (up to four in BTD6) cooperating on a random or private chosen game of BTD5/BTD6 on a chosen map and difficulty. Co-Op Mode is available for iOS and Android several months later, as well as on BTD5 Steam.

Co-Op Mode has first been released to BTD5 Flash in an update released on 26th March, 2013. The player unlocks it upon reaching at least Rank 10. In BTD5, it is only available for up to two players per game. The player may choose a random game based on their preferred difficulty(s) (Easy, Medium, Hard, as well as Impoppable only on BTD5 Mobile) and map difficulty(s) (Beginner, Intermediate, Advanced, Expert, but not Extreme); afterwards, they will wait for another player that matches the selected criteria as the player. Soon, both players will be ready to play their Co-Op Mode game.

Players are limited to placing, controlling, upgrading and selling towers on their half of the map (the left and right halves). This can also provide some advantages, such as Dartling Gun control and banana collecting able to be separately performed by two players simultaneously.

Each bloon popped will earn $0.5 per pop, reserved exclusively for the player who popped the bloon(s), unless he/she sends money to the other player manually. Communicational co-operation is required to request sharing money to each side fairly.

On BTD5, Reverse Mode on tracks is random, unless it is specified for a Private Match. Private Matches can have difficulty, track and direction specified by the player who created the private match.

Co-op Mode is now available on iOS and Android.

Cooperation
This does not apply for Steam version. Only Flash allow players to communicate via chat, which is accessible by pressing the button. Players can also choose to request cash from their partner, sending them the alert MSG: Your ally has requested some cash. Their partner can choose to donate cash to their partner in increments of $0.5 whenever they like, up to $500 or their current amount of cash (whichever is less) every time they donate. Donations can be made to and from both players and are unrestricted in when they can be made and how much total cash can be donated. If a player accumulates more than $5000, they will send $5000 instead of $500.

Maps (BTD5)
There is both a new map and an old map for each difficulty:
 * Beginner: Z Factor, Alpine Lake, Pumpkin Patch, North Pole, Express Shipping, Snowy Backyard, Rabbit Holes
 * Intermediate: Snake River, Haunted Swamp, Jungle, Country Road, Six Feet, Lava Fields, Water Hazard
 * Advanced: The Eye, Cash Money, Candyland, Crypt Keeper, Dune Sea, The Great Divide, Rink Revenge, Scorched Earth, (Long Range and Battle Knot are Bloons TD 5 Mobile exclusive)
 * Expert: Castle, Spider Map, Tree Tops, Down the Drain, Runway

Bugs

 * Only the left player sees the bloons correctly, the right player sees bloons with time delay, so only the left player should use road spikes and dartling guns.
 * The screen will sometimes black out for a second, then the current round will finish, but it is impossible to go on to the next round.
 * On rare occasions, towers will automatically upgrade, and some even into impossible upgrade combinations. An example is a 3/4 Dart Monkey.
 * Sometimes the game freezes and although you can still chat, the game won't play, forcing you to quit. This doesn't happen if the game is lagging.
 * Quite commonly, the round will finish when a low-ranked bloon is still on the track. It will still be able to be popped.
 * On the mobile version, if you and your ally fail, sometimes if both players tap "Yes", another fail message will appear. "You and your ally made it to round: 0". This may result in one or more players forced to forfeit the game.
 * If you use the double cash premium, you will get 4x the cash, starting with $1100.

Trivia

 * Players who own Premium Upgrades will have them activated, but the other player will not be able to gain access to them, with a few exceptions such as Triple Lives.
 * When a game finishes and the player wonders whether to continue, Freeplay Mode can only be played if both players click on the keep playing in freeplay mode button, if one does not want to participate, the game ends. This is not the case in the Mobile version, where if one person selects to continue, they will continue in single player unless the other player also chooses to continue.
 * If the ally disconnects from the game there will be an option to play solo, which is arguably easier than playing Co-op. The player will not get the Co-op medals for completing the track, although the player will receive the full amount of Monkey Money if the medals for that track and difficulty have not yet been earned. If the track is complete in regular single-player mode, the player will earn the medal for single-player mode instead.
 * Due to the prevention of earning Co-op medals, users can "troll" and exit on the last round to disconnect.
 * The Monkeys on the Co-op Mode button appear to have been playing for a long time without sleep, as they have wrinkles under their eyes.
 * Money for popping bloons or rounds is divided evenly among both players, so it is not important who pops more bloons. However, money from Banana Farms or Supply Drop Sniper Monkeys is not shared.
 * If a temple is created, it will sacrifice towers on the other player's side of the map, which might lead to frustration if your opponent was not prepared. However, it can be an aid if one is trying to get a max temple. (Not on Steam Version)
 * Having a matching player when trying to connect will result in a Super Monkey Fan Club sound effect. Then the screen will load to the random track.