The B.O.D is a bloon that has 25,000 more hits to pop than a ZOMG. The B.O.D is the parent of 4 ZOMGs, though it doesn't have a parent, itself. The B.O.D first appears on round 125. The B.O.D can appear on any difficulty, and it is a very deadly bloon.
The B.O.D never gets popped by abilities.