If a bloon reaches the end of a path, the player loses lives (or in later games, health) once these are all depleted, the game ends. The game is a tower defense game and thus the player can choose various types of towers and traps to place around the track in order to defend against the bloons, gaining 1 in-game dollar for every layer of bloon popped.

The main objective of Bloons TD is to prevent Bloons (in-game name for balloons) from reaching the end of a defined track on a map that consists of one or more entrances and exits for the bloons. Money is gained by popping bloons, completing rounds, and collecting bananas from existing banana farms which can be spent on new towers, upgrades for existing ones, or temporary items such as exploding pineapples and road spikes. A handful of towers can stall the bloons and give the other towers more time to pop them by freezing and gluing the bloons. In the game, players attempt to prevent Bloons (the in-game name for balloons) from reaching the end of a set course by placing towers or road items along it that can pop the bloons in a variety of ways, typically by utilizing the power of monkeys. Games in the Bloons series older than Bloons TD 6 are available through the Ninja Kiwi Archive on Steam. Later games in the series expanded to support various mobile platforms, including Android, iOS, Windows Phone, PlayStation Portable, Nintendo DSi, Windows, Linux and MacOS. The game was initially developed as a browser game, built upon the (now unusable) Adobe Flash platform and released in mid 2007. Android, browser (Flash), iOS, macOS, Nintendo DSi, PlayStation Portable, Microsoft Windows, Xbox One, Nintendo Switchīloons Tower Defense (also known as Bloons TD or BTD) is a series of tower defense games under the Bloons series created and produced by Ninja Kiwi.

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