Experience Point Farming

Experience Point Farming, often shortened to XP Farming, is the gaining of experience points quickly or to rank up quickly. Normally, players gain experience points by playing the game more often, if for upgrade experience points, or by popping more bloons, if for Ranks.

XP Generation Totals
In BTD6, higher difficulties and higher level maps (+10%, +20%, +30% for harder maps) gain more XP per round.

XP distribution
In BTD6, the XP is distributed based on the cost of towers, not the number of towers. If there are two towers of one type worth $1000 in total and a different tower worth $1000, then each tower type will receive 50% of the XP.

Method 1: MOAB Madness
Play lots and lots of Special Missions and alternate the use of towers. Play MOAB Madness and use lots of MOAB Maulers, some Arctic Wind and several Glaive Riccochet, and perhaps a few Ice Shards too. With spare money, place in a few towers that you want to have extra Experience Points with, and they should be able to unlock new upgrades each time. If you want to speed the amount of experience to over-the-top amounts, which has the capability to unlock 5 upgrades in one game, then use all of the spare money by spamming the type of tower you want to gain tons of experience.

Note: Does not work for Monkey Buccaneer or Monkey Sub, unless you are willing to spend some Monkey Money to buy Portable Lakes to exploit the experience earning process.

Method 2: Regrow Farm
One way to gain ridiculous amounts of Experience Points quickly is to Regen Farm. Popping enough bloons will gain ranks much faster. The looping will gain experience to rank up quickly. Add more random towers for the towers' own experience gain. Requires advanced Monkey Apprentices, Ice Monkeys and among several others. This method no longer works for Bloons TD 5 Flash, as Ninja Kiwi made it so that you don't get xp from popping bloons. This works for the Mobile & Steam version.

Method 3: Beginner Maps on Easy
Play an Beginner Track on an Easy Difficulty and spam in towers that you wish to develop. Add vital towers to support as well to avoid losing the game. Somehow, you need to find a way to increase the number of the target developing towers and at the same time avoid losing the game. It may be easy to develop Dartling Guns, but it may be more difficult to develop Super Monkeys in this method, as Super Monkeys are very expensive.

If you want to develop water-based towers, try playing Park Path.

Method 4
Play more of the Daily Challenges Third Time's A Charm (July 2nd, 2012), The Daring Dozen (January 27th 2014) or 20 Ceramics on the Wall (July 30th, 2012). Playing 20 Ceramics on the Wall Rounds 1-70 can earn around 5000 XP each time, and The Daring Dozen can give lots of XP on rounds 37-39, 49, and 61.

Method 1: Deflation
Play on any Sniper-viable map, especially Infernal (gains +30% XP compared to Beginner Maps), and use a 2-0-2 Village, 4-2-0 Alchemist, and 0-2-4 Sniper. Then add any other towers around the map. Gains player XP quickly and simply.

Method 2: Deflation (Alternate)
Place a 4-0-0 Alchemist and a 4-0-1 Ninja towards the start of the map, and fill the rest of the map with the desired tower. The lower cost of the Ninja and Alchemist allow for more XP to be allocated to the target tower.

Method 3: Playing trivial ACs
If lucky, a trivial AC can be played over and over again to gain a huge amount of XP. A notable example is the previous 4th/5th March 2022 AC "111111 Against 265", accumulating more than double the XP compared to deflation mode on Infernal.