From Ninja Kiwi:
Stop any Bloons from escaping the maze by building and upgrading bloons popping towers. Throw darts, tacks, bombs and ice. Can you make it through all 50 levels? Game Instructions: Click on the tower type you want to build on the right side of the screen, then once its selected, place the tower in the maze. Press escape to deselect or cancel your current action. You can sell towers for extra money for 80% of what you paid for them. Larger colored bloons have smaller bloons inside them, so watch out.