Steel Bloon

The Steel Bloon is a bloon conception that appears on round 55 and up, replacing regular lead bloons. Unlike regular lead bloons, it has 10 layers to pop, rather than 1, like a ceramic bloon. In fact, it has a lot in common with the ceramic bloon. It has a slow destroying animation, like the ceramic bloon, and towers that deal extra damage to ceramics (at least the ones that can pop leads) will deal extra damage to the steel bloon too.

Strategies
When dealing with steel bloons, it is best to use towers such as the spike ball factory & juggernaut to deal with them. However, for continued survival, you may have to get a bit more expensive and use a 2+-X plasma monkey or 2 to deal with them. It is also a good idea to make sure that your steel-bloon popping towers can also pop camos (Using a monkey village, or upgrading), as shortly in round 59, there will be 28 camo leads, and around half of those will be chosen as steel bloons instead, making them camo. However it is safe to sell the monkey village after round 85, as ceramic bloons will never be camo during randomly generated rounds.