Indestructible

Indestructible is a new bloon property in the next Bloons Tower Defense game. Bloons with this property cannot be destroyed in any way, but only come in high-numbered rounds. Most of the time, they cause you to lose numbers of lives that bring your total lives down to a specific number, thus helping to make the game harder (for example, even if you've somehow gotten up to 1000 lives, you could suddenly be down to 50).