Bloons Tower Defense

Before the rise of man brought the great rivalry between Pirate and Ninja, there was another natural feud between two animal species: Monkeys... and B[al]loons. No one knows how or why this epic war began, but both sides fight endlessly with ever greater wartime developments vying for domination of the world. All of the preceding is included absolutely nowhere in the game's design, and is merely a flavorful fantasy explaining why players seem to care so much about using monkeys to pop balloons.

Bloons Tower Defense (or BTD as it's abbreviated) is an ongoing Tower Defense series by NinjaKiwi where monkeys (and other weapons) are used to pop a seemingly endless line of overly determined balloons of varying shapes, sizes, and speed. Though starting out with a simplified design palette, later editions of the game have evolved to include a great deal of complexity in both art and gameplay mechanics.

This game was a spinoff of the lesser known Bloons (a series of aim-and-power-meter puzzle games with many player designed maps), but became so much more popular that this series got its own spinoff, Bloons Super Monkey (a top-down aerial shooter starring the titular monkey from the BTD series).

All versions of the game can be played at NinjaKiwi's site and the original BTD(which is actually BTD3) and BTD4 are available on the iPhone.

The games provide examples of the following:

The Adventure Continues: BTD3, 4 and 5 allows you to keep playing in free mode after you beat the 50, 60, or 75 levels of bronze, silver, and gold gameplay respectively.
Allegedly Free Game: The later versions are technically winnable without shelling out for all the various upgrades a player can buy (more lives or in-game money, faster shooters, etc.) but you have to get everything exactly right.
Anti-Poopsocking: "Remember to occasionally take breaks and do non-BTD5 things."
Area of Effect: The Tack Tower's specialty.
Art Evolution: BTD2-BTD3 used the same art for Bloons introduced in previous games, but the shift to BTD4 improved the graphic, and the art drastically changed for BTD5
Asteroids Monster: Several of the stronger bloons will unravel weaker ones when popped.
Awesome but Impractical: The Monkey God Temple in 5. It fires enormous beams calable of tearing anything less than a BFB to shreds, but it costs a whopping $125,000, since you have to buy laser, plasma, AND the Sun God to even access it. (And that's without the range powerups- counting those, the price goes up to $127,500.) Not exactly worth it when you could get five Sun Gods for the same price. (And five Sun Gods will mow down just about anything the bloons can throw at you.)
Beam Spam: Super Monkey? Meet Sun God Monkey. Sun God Monkey? Meet BTD5's Sun God Monkey Temple.
Big Bad: The Z.O.M.G., arguably.
Blatant Lies: In BTD5.

Next level will be fun. A whole bunch of ceramic bloons are going to charge right through your defenses and pretty much make you lose.

Boring but Practical: Banana Farms are expensive and don't attack Bloons, but they give you extra money, which you will need in later levels when the Bloons themselves earn you less money.
Boss in Mook Clothing: M.O.A.B.s, natch. To wit- they contain four ceramic bloons, each of which contain two rainbow bloons, which were the highest Bloon rank in BTD4. Furthermore, they cannot be slowed down and are resistant to the Super Monkey Storm.
- Ceramic bloons can also be considered as this, as they take more hits to destroy than any other bloon (other than the M.O.A.B.). All weaker bloons can only take one. BTD5 notes that it takes eighteen shots to drop a single ceramic to completely popped. Eight of those are just to crack the shell.
- And then there are B.F.B.s. Even more health than the M.O.A.B. and also cannot be slowed down. They contain M.O.A.B.s.
- Bloons Tower Defense 5 has an even bigger unit than the B.F.B. (the ZOMG Bloon).
Boss Rush: Level 75 of BTD4, the final level of Hard mode on any course.

"This is the true final level. You know it's going to be all B.F.Bs and M.O.A.Bs right?"

Contractual Boss Immunity: M.O.A.B.s and B.F.Bs are immune to slowing down as well as the Super Monkey Storm (otherwise a One-Hit Kill).
- In BTD5, there are a few special abilities which do nothing except for destroy a single M.O.A.B.-class bloon. However, the Z.O.M.G., while not completely unaffected, will only take 1000 damage.
Easy Mode Mockery: The picture for easy mode BTD4 onwards is a baby monkey.
Everything's Better with Monkeys: A basic tenet of the game.
Eye Beams: The Super Monkey uses these as an upgrade.
Fun with Acronyms: The M.O.A.B., also known as Massive Ornary Air Blimp. As for B.F.B., it's Brutal Floating Behemoth.
- And the Z.O.M.G. is the Zeppelin Of Mighty Gargantuanness.
- One stage in BTD3 has the hint "MOAB stands for Massive Ornary Air Blimp, not Mother Of All Bloons. Either way, it brings pain."
The Goomba: Red Bloons.
Invisible Monsters: Camo Bloons aren't really invisible, but most towers will not be able to detect them unless there is a specialized tower nearby.
Magikarp Power: The tack shooter. In the beginning, they really Can't Catch Up. Once you unlock ring of fire, however...
- Dart Monkeys in BTD 5. They are towers that might be pathetic. Then you use the Super Monkey Fan Club Ability...
Meta Powerup: In BTD4the banana farms/plantations/republics/research facilities give the player extra money after they complete a level.
Won't Work On Me: Black Bloons are immune to explosives, White Bloons cannot be frozen, Zebra Bloons have both the properties of black and white, and Lead Bloons cannot be damaged by sharp objects (And Super Monkey lasers, sans Plasma and the Sun God, prior to BTD 4). The M.O.A.B and B.F.B are immune to anything that slows them down, as well as the Super Monkey Storm, of course. The Z.O.M.G. will merely take 1000 damage from one of the Bomb Tower's maulers in BTD5 if the ability is unlocked and activated.
Oh Crap: Watch the end of the BTD 5 trailer...
One-Hit Kill: The Super Monkey storm. Works on everything except for M.O.A.B-class bloons.
- If a M.O.A.B.-class bloon slips through your defenses, you instantly lose. Those things will eat up your remaining stock of lives.
- Plus,the MOAB takedown ability in BTD5 will reel in a bloon, the strongest being the B.F.B. (They are supposed to aim at M.O.A.Bs and B.F.Bs).
Precision F-Strike: Round 14's tip on the Super Monkey.
Precision-Guided Boomerang: Actually averted with the Boomerang monkeys, their boomerangs go in a set circular path (although they will try to throw it at the bloons).
Regenerating Health: BTD5 gives us Regenerating Bloons: Heart-shaped bloons which, if left unpopped, restore themselves to their original color.
RPG Elements: For most of the series, you only needed enough money to afford the next upgrade. With BTD4, ranks must be earned to unlock all of the towers and top tier upgrades.
- In BTD5, however, all upgrades and towers must be unlocked. Both can be unlocked through rank-up, but a tower will need experience in the case of the former. Another case of the former is that rank-up only unlocks the final upgrades of the towers.
Smart Bomb: The radar tower can be upgraded to call in a bunch of super Monkeys, which insta-kill every single bloon on the screen. Except M.O.A.B-class bloons.
Spikes of Doom: Tacks/road spikes can be placed on the floor, and will do pop 10 bloons before disappearing.
Spike Balls of Doom: The spike catapult launches these.
Splash Damage: Many upgrades give towers this ability, but Tack Towers and Cannons have it as their bread-and-butter.
Spread Shot: Sun God Monkeys have a rapid piercing 3-way eye beam, while Monkey Buccaneers can be upgraded to have a 5-way shot.
Standard Status Effects: While most towers are designed only for destruction, a few specialized abilities are required by some.
- Cannons and other explosives are needed to pierce Lead Balloons.
- Ice Towers can freeze bloons in place, and even slow them down permanently with the Permafrost upgrade.
- Glue piles (and in later versions Glue Monkeys) slow down the fast-moving bloons that spell instant death.
- Glue Monkeys with corrosive glue can also give the bloons an effect similar to poison, while slowing them down at the same time.
- Radar towers expand the range and fire rate of towers, as well as allowing them to see camo bloons.
Stealth Mook: The Camo Bloon, which first appears in Bloons Tower Defense 4. In its initial appearance, it is around the same level as Black and White Bloons, and can only be actively targeted by a tower or monkey with camouflage detection - they can still be hit and popped by collateral damage from area-of-effect attacks. Bloons Tower Defense 5 and 6 make Camo a "trait" applicable to any non-MOAB Bloon, and Camo Bloons cannot be targeted or damaged by towers without camo detection.
Tech Tree: Sort of. BTD5 handles upgrades differently to the previous games - each tower now has two upgrade paths that can be chosen from. You can go two upgrades down both paths without penalty, but after you pick a third upgrade from either, you can no longer go beyond the second upgrade from the path you didn't pick.
Tetris Effect: Best to stay away from carnivals and parties after playing this game for too long.
Zerg Rush: Sorta of the entire methodology of the Bloon hordes; each higher grade bloon contains so many of the next class down. Sending a whole bunch at one time is what amounts to "difficulty" in the game.