Here is the full list of all 71 Bloons Adventure Time TD achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Pop a BAD
Use 5 Powers
Buy 100 Upgrades that Require another Character
Open 200 Wish Orbs
Pop 10,000 Ceramic bloons
Pop 100,000 bloons using Supermonkey
Pop 1,000 MOAB bloons
Pop 100,000 bloons using Sai
Pop 100 BFB bloons
Pop 5,000 Ceramic bloons
Promote a Character to 5 Stars
Open 150 Wish Orbs
Pop 100,000 bloons using Sam
Pop 1,000,000 bloons
Pop 100,000 bloons using Ice King
Pop 500 MOAB bloons
Pop 50 BFB bloons
Complete 20 Adventures
Pop 100,000 bloons using Finn
Open 100 Wish Orbs
Pop 1,000 Ceramic bloons
Buy 50 Upgrades that Require another Character
Pop 100,000 bloons using Flame Princess
Promote a Character to 4 Stars
Complete 15 Adventures
Pop 100 MOAB bloons
Have Finn, Flame Princess, and Princess Bubblegum on the map at the same time
Complete 10 Adventures
Open 50 Wish Orbs
Pop 250,000 bloons
Pop 25,000 bloons using Allies
Pop 1,000 Lead bloons
Place Cassie on an underwater map
Complete 7 Adventures
Buy 20 Upgrades that Require another Character
Open 25 Wish Orbs
Promote a Character to 3 Stars
Complete 5 Adventures
Pop 500 Lead bloons
Pop 5,000 bloons using Allies
Pop 200 Lead bloons
Pop 50,000 bloons
Open 10 Wish Orbs
Complete 3 Adventures
Pop 500 bloons using Allies
Open 5 Wish Orbs
Promote a Character to 6 Stars
Promote a Character to 7 Stars
Promote a Character to 8 Stars
Promote a Character to 9 Stars
Promote a Character to 10 Stars
Fully Equip a Character
Pop 500 BFB bloons
Use 10 Powers
Use 25 Powers
Use 50 Powers
Use 100 Powers
Use 200 Powers
Use 300 Powers
Use 400 Powers
Use 500 Powers
Pop 100,000 bloons using Allies
Pop 100,000 bloons using Jake
Pop 100,000 bloons using Princess Bubblegum
Pop 100,000 bloons using Marceline
Pop 100,000 bloons using Max
Pop 100,000 bloons using C4 Charlie
Pop 100,000 bloons using Captain Cassie
Become the Sun God
Have the Monkey Apprentice, the Sniper Monkey, the Dart Monkey, and the Boomerang Monkey on the map at the same time
Buy the Treasure Hunter Upgrade