Parasitic Bloon

The Parasitic Bloon is a microscopic bloon that can get inside one of your towers without you knowing it. The only way for you to realize that it's there is by seeing that the infected tower is losing 1 health point every 10 seconds (on top of any other damage it is taking). It stays inside the tower until the tower is either upgraded or destroyed (fully upgraded towers are too powerful for it to infect). If an infected tower is upgraded, the bloon is destroyed and the tower regenerates any health that was damaged by the bloon (but still has any damage that came from other sources). It is possible to go on to another round without doing anything about the bloon, and it will not do any damage between rounds (but it will remain in the tower and will begin doing damage again after the next round starts).