Bloons Tower Defense 2 (also known as BTD2 or Bloons TD 2) is the sequel to the original Bloons Tower Defense, and the prequel to Bloons Tower Defense 3. It introduces Difficulties to the Bloons TD series. There are new additions to every category - Bloon types, Towers, Tracks, and a new upgrade for the Super Monkey called Laser Vision. After finishing each Difficulty, you earn a medal for it.
- Red Bloon: The first bloon in the game. RBE: 1
- Blue Bloon: A tiny bit harder to pop. Contains 1 Red Bloon. First appears on Round 3. These bloons are faster than Red Bloons. RBE: 2
- Green Bloon: Yet again, a little harder than the previous bloon. Contains 1 Blue Bloon. First appears on round 6. Green Bloons are faster than Blue Bloons RBE: 3
- Yellow Bloon: Fastest bloon in the game. Contains 1 Green Bloon. RBE: 4
- Black Bloon: Speed of a Green Bloon. Contains 2 Yellow Bloons. It is immune to bombs. RBE: 9
- White Bloon: Very similar to the Black Bloon. Contains two Yellow Bloons. It is slightly faster than a Black Bloon. It is immune to ice. RBE: 9
- Lead Bloon: It is immune to sharp objects. Explosions work best against it. Contains two Black Bloons. These bloons are the speed of a Red Bloon. This bloon is the reason it is impossible to win BTD2 using only Dart Monkeys and/or road spikes. RBE: 19
- Rainbow Bloon: Strongest bloon in the game. These bloons are slightly faster than White Bloons, but slower than Yellow Bloons. Contains 2 Black Bloons and 2 White Bloons. RBE: 37
- Dart Monkey: A monkey that throws darts
- Tack Shooter: Shoots out tacks in 8 directions
- Ice Ball: Freezes bloons in its radius.
- Cannon: Shoots bombs that explode when bloons are hit.
- Super Monkey: The hypersonic monkey from Bloons TD 1. Shoots darts extremely fast.
- Boomerang Thrower: Throws boomerangs in a loop back to the monkey, popping bloons along the way.
- Road Spikes: A pile of 10 tacks that can pop up to 10 bloons when placed along the track. They can't pop Lead Bloons.
- Monkey Glue: A glob of glue that slows bloons as they pass through. They can slow down up to 20 bloons.
In Bloons TD 1 and Bloons TD 2, there is a glitch involving the Tack Shooter/Tack Tower. The player has to buy a Tack Shooter and then keep pressing Tab on the keyboard until you reach Faster Shooting. Then, keep pressing space-bar (4 is enough), and the Tack Shooter will shoot at hyper-sonic speed. However, if the player has insufficient cash to buy those "extra" upgrades, they get negative cash and become unable to purchase anything else except upgrades (using this glitch). However the player can still gain money by popping bloons and getting rewards at round endings. This glitch also works on some other upgrades, such as range upgrades for monkeys like the Bomb Tower (it doesn't work on the Tack Shooter's range upgrade though).
- Road Items made their debut in this game.
- The only major change with towers are the addition of road items and the boomerang thrower.
- In the Boomerang description, there's a typo that says "Sonic booom upgrade" instead of "Sonic boom upgrade". It's very likely to be a writing error.
- The Dart Monkey without upgrades can already pop 2 bloons with one shot even though it says 1.