Sometimes throws a flash bomb that stuns bloons in a large radius.
~ In-game description
This is the third upgrade of path 2 for the Ninja Monkey. It can stun and pop up to 60 bloons. This upgrade is not recommended for popping camolead bloons, unless it's the only way on a daily challenge, due to the cheaper cost of the Monkey Apprentice, and the Monkey Apprentice's faster firing speed. It turns the ninja dark grey with a red bandanna.
Flash Bomb Ninja Official Artwork
Ninja Monkey with Flash Bomb Upgrade
Ninja Monkey throwing a Flash bomb
Flash Bomb Icon
Flash Bomb icon in Bloons Monkey City
Flash Bomb Ninjas vs Ceramic Bloons in Bloons Monkey City Mobile (click for better view)
Stunning bloons with Flash Bomb (by black-clothed ninjas)
For some, the stun effect is how the price is worth it, through, while not as efficient as Bloon Impact, it can hold off until the user can buy it. However, Bloon Impact needs some camo support while this doesn't need any.
In Flash, the bomb has a unique sprite. But in the mobile versions, the bomb sprite used for the Bomb Tower is used for this upgrade.
This makes the Flash Bomb especially useful in BTD Battles, as the opponent can send in camo leads on Round 12 (of course, that's just for starters. Other upgrades cost a lot less.)