Board Thread:Bloons Wiki and BTD News/@comment-24243160-20140222131805/@comment-24243160-20140227120725

You have to spend a certain amount of energy (10 for Village, 12 for Mortar) to use them. They can't be moved, and can be left anytime, but if you return to use them, you won't have to use any energy. Village will provide boosts to nearby monkeys/towers in a range for 4 tiles in every direction, while Mortar can harm bloons from far away, and even reduce the amount of current energy from players.