They're Back! is the name of a special round that takes place toward the end of the next Bloons Tower Defense game. In this round, all of the bloons that escaped in previous rounds return, and you must defeat them. However, they will now be Overpowered, having double their normal health and power. Obviously, the difficulty of this round may vary depending on how many bloons escaped. If you haven't let any bloons escape up until this point, this round will be skipped automatically.