Well, the Bloonsday device is a special agent. It costs 250 MM to buy, and it is a one time use in a level, challenge, or mission.
It does not attack bloons but gives an ability called “Orbital Strike”. The in-game description: Creates a beam that destroys all bloons and does big damage to MOAB-class bloons. But what it really does: The beam follows your mouse cursor and destroys non-MOAB class bloons when it encounters them. The beam lasts for about 10 seconds.