Ever since the first Bloons TD game, the Bloons have aspired to do one thing: take over the Monkey Kingdom using sheer numbers (with the exception of Bloons Adventure Time TD, in which the Bloons attempt to invade the Land of Ooo instead). Their origins and motives remain a mystery, though it's likely that the Bloons may want the monkeys' land for the purpose of using its resources to create more of themselves. In the effort to seize the Monkey Kingdom from its rightful owners, the Bloons pose two main threats, the first of which is their ability to rush their opponents with large groups, allowing them to easily overwhelm an underprepared defense force in time. The second threat the Bloons pose is their technological prowess; with each new entry in the Bloons TD series, the Bloons are seen introducing new, more advanced units to their ever-expanding army, each one imbued with special properties that provide protection against the monkey defenders in some form or another. Despite these traits, however, the Bloons are not an intelligent species. Their seemingly infinite capacity for improving their units is compromised by the fact that they are terrible strategists. The Bloons rarely if ever deviate from their usual tactic of rushing the monkeys in organized waves, starting with their weakest grunts and slowly working their way up. This, coupled with the fact that the monkeys are also able to upgrade their own defenses, results in the Bloons constantly losing out to their furry rivals so long as the monkeys are adequately prepared.
These are the standard Bloon units. They come in many varieties, each with its own special properties.
- Red Bloon: First appearing in BTD1, this is the most basic Bloon type. It moves slowly and can be popped in just one hit.
- Blue Bloon: First appearing in BTD1, this Bloon moves a little faster and spawns a Red Bloon when popped.
- Green Bloon: First appearing in BTD1, this Bloon moves at moderate speed and spawns a Blue Bloom when popped.
- Yellow Bloon: First appearing in BTD1, this Bloon moves quickly and spawns a Green Bloon when popped.
- Pink Bloon: First appearing in BTD4, this Bloon moves very quickly and spawns a Yellow Bloon when popped.
- Black Bloon: First appearing in BTD1, this Bloon is immune to explosives. It used to spawn two Yellow Bloons when popped, but as of BTD4 it now spawns two Pink Bloons.
- White Bloon: First appearing in BTD1, this Bloon is immune to ice attacks. It used to spawn two Yellow Bloons when popped, but as of BTD4 it now spawns two Pink Bloons. It also moves slightly faster than a Black Bloon.
- Purple Bloon: First appearing in BTD6, this Bloon is immune to fire, energy, and magic attacks, making it quite dangerous at higher levels where most players tend to start relying heavily on energy-based towers. It spawns two Pink Bloons when popped.
- Zebra Bloon: First appearing in BTD4, this Bloon is immune to both explosive and freezing attacks. It spawns a Black Bloon and a White Bloon when popped.
- Lead Bloon: First appearing in BTD2, this Bloon defies the laws of physics. It's made entirely of metal and moves very slowly, but is immune to attacks with blades or sharp objects, as well as wind attacks that push most other Bloon types further away from the level's exit. It spawns two Black Bloons when popped.
- Rainbow Bloon: First appearing in BTD2, this Bloon moves more quickly than most others and originally spawned two Black Bloons and two White Bloons when popped. As of BTD4, though, it now spawns two Zebra Bloons.
- Ceramic Bloon: First appearing in BTD3, this Bloon is made of clay and takes 10 hits to pop instead of just one. It spawns two Rainbow Bloons when popped, and as of BTD4 it also can't be slowed down by glue weapons (but it can still be affected by corrosion if the Corrosive Glue upgrade has been applied).
- Super Ceramic Bloon: First appearing in BTD5, this Bloon looks identical to a normal Ceramic Bloon and has most of the same properties; it takes a whopping 60 hits to pop but only spawns one Rainbow Bloon when popped.
These are the Bloons' secret weapons. They are massive blimp-like monstrosities that take numerous hits to be destroyed, are immune or resistant to many types of attacks, and carry so many smaller Bloons inside of them that just one escaping will instantly end the game.
- Massive Ornary Air Blimp (MOAB): First appearing in BTD3, this was the first Bloon of its kind, and also the namesake of its class. It moves slowly but takes 200 hits to pop and is immune to glue and ice attacks. It spawns four Ceramic Bloons when popped.
- Brutal Floating Behemoth (BFB): First appearing in BTD4, this Bloon moves more slowly but takes 800 hits to pop and is also immune to glue and ice attacks. It spawns four MOABs when popped.
- Zeppelin of Might Gargantuaness (ZOMG): First appearing in BTD5, this Bloon moves even more slowly but takes 4000 hits to destroy, is immune to glue and ice attacks, and only takes partial damage from special abilities that kill lesser MOAB-Class Bloons instantly. It spawns four BFBs when popped.
- Dark Dirigible Titan (DDT): First appearing in Bloons Monkey City (a spinoff of BTD5), this Bloon is a strange hybrid among the MOAB-Class Bloons. It only takes 400 hits to pop but moves very quickly (it used to move as quickly as a Pink Bloon in Bloons Monkey City, but as of BTD6 it's slightly slower than a Purple Bloon), is immune to explosives and sharp objects like lead and black Bloons, and has the Camo property. It spawns six Ceramic Bloons that have Camo and Regrow properties when popped in Bloons Monkey City and four in BTD6.
- Big Airship of Doom (BAD): First appearing in BTD6, this is currently the most powerful Bloon to date. It moves extremely slowly but takes 20,000 hits to pop, is immune to any attacks that hinder Bloons' movement, only takes partial damage from special abilities that kill lesser MOAB-Class Bloons instantly, and spawns two ZOMG and three DDTs when popped.
The Boss Bloons are a group of especially powerful MOAB-Class Bloons that, unlike the rest of their bloated brethren, have unique identities and abilities. They appear in Bloons Monkey City as the bosses of certain special events in the game and in Boss events in BTD5 for Steam/Mobile. None of them spawn any other Bloons when popped.
- Bloonarius the Inflator: A swamp-dwelling MOAB-Class Bloon that has most of the same properties as a ZOMG, but moves even more slowly and has far more HP. At specific health intervals, he can also spawn other Bloons; the Bloons he summons can range from Lead Bloons to ZOMGs depending on how high his boss level is.
- Dreadbloon, Armored Behemoth: An earth-based MOAB-Class Bloon that can generate stone armor to protect himself from getting hit. He has the same properties as a Lead Bloon (but the armor doesn't).
- Vortex, Deadly Master of Air: A sky-themed MOAB-Class Bloon that periodically releases shockwaves that can stun or slow down the fire rate of your towers.
- Blastapopoulos, Demon of the Core: A fire-themed MOAB-Class Bloon that can shoot fireballs that stun your towers. He always targets towers that have been the most heavily upgraded, and automatically shoots a fireball whenever a tower is sold regardless of his normal fire rate.
In addition to engineering Bloon types that can resist certain types of attacks from the monkeys, the Bloons can also further enhance themselves with Bloon Properties that grant them additional powers which make them even harder to pop. Most of them can't be applied to MOAB-Class Bloons, though.
- Camo: Interestingly, this property originated as a standard Bloon unit in BTD4. Its camouflaged pattern made it invisible to any tower that wasn't upgraded to have Camo Detection, and it spawned two Pink Bloons when popped. As of BTD5, Camo is now a Bloon Property that can be applied to any type of Bloon.
- Regrow: First appearing in BTD5, this property allows Bloons to regrow their layers after being popped if left alone for too long. Regrow Bloons are shaped like hearts.
- Fortified: First appearing in BTD6, this property doubles the amount of hits it takes to pop Bloons with the property. Fortified Bloons have metal bands wrapped around them. Unlike most other properties, this one can only be applied to certain Bloons - those being Lead Bloons, Ceramic Bloons, and MOAB-Class Bloons.
- Shielded: First appearing in Bloons Adventure Time TD, this property applies a personal force field to Bloons that takes five hits to break. Shielded Bloons have a lightning bolt symbol on them.
- Zombie: First appearing in Bloons Adventure Time TD, this property allows Bloons to respawn in their original form in the next round after being popped for the first time. When a Zombie Bloon is popped, a tombstone appears where it was popped, indicating where it will respawn in the next round. Zombie Bloons have stitches all over them.
- Ghost: First appearing in Bloons Adventure Time TD, this property makes Bloons immune to physical attacks. Ghost Bloons are covered by a ghostly drape. This property can be applied to MOAB-Class Bloons too.