Helium Bloon

The Helium Bloon can spawn anywhere on the map, and takes 250 hits to destroy. After spawning, it slowly floats upward (toward the camera - or whatever it is - that shows you what is happening in the game). As it floats up, it expands (because the air pressure is lower), and if it is not destroyed quickly, it will start blocking your view of parts of the game area. Once it reaches a certain height, it is out of ground towers' range, and can only be attacked by aerial towers (such as Monkey Aces). If it manages to hit the camera (at which point it would be blocking the whole screen), it pops, causing you to lose 25 lives and have cracks appear randomly over the game area (because the camera's lens is cracked). If the camera gets cracked, it stays that way for the rest of the game, and the cracks can get worse if it is hit more times.