4 3 2 1 boom is the thirty-eight level in Bloons Player Pack 1.
To complete this level, you need to make your dart have a decently high power, and try to aim accurately for the Tack Bloons. If you aimed very accurately, the dart will be able to pop the Bomb Bloons.
- It is called "4 3 2 1 boom" because the dart bounces 5 times. In the first 4 times, it bounces to pop the tack bloons, while in the last time, it pops the bomb bloons.