Lifelink

A lifelink is an item that can be purchased in the next Bloons Tower Defense game for $5000. It has a "donor" end and a "receiver" end. You must attach each end to a different tower when you purchase it. When placed, if the tower on the receiver end ever loses any health, it regains it by taking health from the donor end (which effectively loses the health instead). The lifelink cannot be removed, so once it is placed, it will not go away unless the donor tower is destroyed (either through normal damage or through having all of its health drained). Multiple lifelinks (either donor or receiver ends) can be connected to the same tower, and chains of lifelinks can be made as well (connecting one tower to another tower, which is connected to another tower, and so on). However, lifelink loops cannot be created.