Bloons Tower Defense: The Lost Ones is, well, a game. It plays out like normal, but there's a new mode: Shattered Glass, which provides history and things such as that. There are 3 paths with 5 upgrades each. Each path is different in a sense. Path 1 is generic upgrades, Path 2 is generic upgrades unique to the tower, and Path 3 is just unique upgrades. (Path 1 is things like range, Path 2 is things like popping leads or different projectiles, Path 3 differs from tower to tower.)