The Monkey Satellite is a tower that requires the Monkey Aerospace Administration to exist, but it is well worth it. By default, all it does is target a very wide area with microwave radiation that pops one layer from bloons every 1.5 seconds. It costs $750 on Medium, and cannot be destroyed (Not even by One Nuke Wonder!), mostly because, well, it's orbiting the planet and stuff. Of course, unlike regular towers, this tower functions off of BTD4 logic - it has one upgrade path.