The S.A.N.S. (Super Amazing Nigh-Invincible Skeleton) is a M.O.A.B. class bloon that takes 1 hit to pop. However, it can only be hit if a tower is under the influence of a Monkey Intelligence Bureau. Furthermore, it travels at twice the speed of a pink bloon. Once it is popped, it releases four black bloons and four white bloons.
Bloons Conception Wiki