Monkey Money

 ( in BTD5, in BTD6) or MM is the secondary currency in Bloons TD 5 and Bloons TD 6. The player can earn it by completing tracks or buy it in sets (10 or $1.99 USD minimum). Once a track is completed and Monkey Money is awarded, and the player completes the same track on the same difficulty again, only 20% of the original reward is awarded. If the player loads a game that was previously finished, the player is unable to get another reward. As of now, Monkey Money can buy Special Agents, Powers (BTD6), play tracks with the Extreme Difficulty level, buy land for and build/upgrade Specialty Buildings, unlock Fast Track Mode, and buy single-use Premium Upgrades. Currently there are 3 Extreme Difficulty tracks: Bloontonium Lab, Tar Pits & Main Street.

BTD5

 * An update was released on Jan 19, 2012 that added a Treasure Chest to the game's main menu that, once clicked, gives the player a random amount of Monkey Money once a day (if you have a Ninja Kiwi account). You can also earn Monkey Money by completing Special Missions.
 * An update was released on Jan 27, 2012 that added the ability to earn Monkey Money for completing Daily Challenges.
 * An update was released on April 23, 2012 that added the ability to earn Monkey Money by 20% reward instead of original reward (100% reward) for replaying all Tracks.
 * On April 26, 2012 there was a update for double Monkey Money. You would get double monkey money every time you win a game, Daily Challenge or Special Missions. You also get double from the treasure chest. This ended April 29, 2012.
 * An update was released on the July 12, 2012, that allowed for a Treasure Chest Monkey Money reward multiplier.
 * Double Monkey Money came again from August 25, 2012 to August 27, 2012.
 * Double Monkey Money came yet again from October 4, 2012 to October 7, 2012.
 * Double Monkey Money came a fourth time from October 25, 2012 to October 28, 2012.
 * Double Monkey Money came a fifth time from December 19, 2012 to January 8, 2013.
 * (Bloons TD 5 Mobile only) On April 18, 2013, this is the first time Double Monkey Money came.
 * Double Monkey Money came a second time for iOS from July 3, 2014 to July 7, 2014.
 * During the Christmas season of 2015, Double Money came again for Flash.
 * Double Monkey Money came again on 23rd March 2016 and ended on 30th March 2016.
 * (BTD5 Mobile only) April 1st 2018 was another Double Monkey Money day, to celebrate the Easter season.

BTD6
There have so far been no updates regarding bonus Monkey Money. However, there have a very few updates on a few select Race Events regarding cheaper speedups.

Playing a Game
The player can obtain Monkey Money by playing a game. Below is an example involving Beginner Tracks. However, if a player already has completed a game mode in a specific track, the reward will divide by 5.

Daily Prize
The player can also obtain Monkey Money from playing BTD5 daily. The more they play, the higher the reward is.

Spending
Monkey Money can be used for building Specialty Buildings, hiring Special Agents and purchasing one-time Premium Upgrades. Also every play of Extreme Difficulty tracks costs Monkey Money.

There is a game option, which requires some Monkey Money in order to unlock.

Playing a Game
Beating maps earns Monkey Money. Like BTD5, harder maps on harder difficulties earn more Monkey Money, and first-time completions reward substantially more. Winning on maps can earn even more Monkey Money if the "Mo' Monkey Money" MK is purchased and active.

Daily Prize
The Daily Chest may occasionally reward Monkey Money, ranging from 50 to 200.

Spending
The player can spend it on purchasing more Powers, using Continues, unlocking additional Heroes, unlocking Hero skins, unlocking deeper Monkey Knowledge Points, and for re-entering Race Events more than once every 4 hours. There are currently no other uses for Monkey Money, although more varieties of uses for Monkey Money may be added in future updates.

Trivia

 * It looks like an American dollar bill in real life, except they have a monkey (apparently named George Monkeyton) on them.
 * George Monkeyton is a pun on George Washington, the first president of the United States.
 * It's much easier to get Monkey Money on BTD5 Deluxe/Steam, as many rewards are twice what they are on the online version in addition to four times the reward for Special Missions.
 * Speaking of BTD5D, you can get permanent premium upgrades by using Monkey Money instead (Though much more expensive)
 * In iOS versions of BTD5, the player can get Monkey Money by opening the chest everyday.
 * If the player goes to their devices settings, then Date and Time, they can change the date. Changing the date makes the iOS or Steam version of TD5 think that it is a new day, so the player can then open the chest multiple times everyday, giving the player "Unlimited Monkey Money."
 * However if you do this and set the time back to normal the chest cannot be used until the actual "day" comes.
 * In BTD6, the Monkey Money icon is named "BloonjaminsIcon.png" in the files.