Bloons Tower Defense is a browser game in which balloons move along a path and the player must keep them from reaching the end of the path. As the game progresses, players pay in-game money to upgrade their towers to defend the land along the paths.
Movement's Relationship With Player Agency
Players place different types of towers across the map that they unlock with money
Movement is the main system in Bloons Tower Defense along with its Upgrade system. In the movement system, the units moving through it are the player-controlled towers that the player can place, the opposing balloons that move along the level path, and the real time projectiles that some towers shoot at the balloons.
Hoards of balloons move at a constant pace when players start each level
The balloons are not player-controlled and they serve as an enemy the player must destroy and keep from advancing. The movement of the balloons don't provide player agency because the player does not control their movement. The balloons move in real time along a constant path; there are no visible discrete spaces along the path.
The experience intended with the balloon movement system is that the player has to judge the balloons' movement to decide where to place and when to use their towers or obstacles. The movement of the balloons is the driving force of the game's challenge. This system intermeshes with the projectile system and popping systems since movement of the balloons is affected by them.