Prepare for Challenge Monkey! An all new, limited time event that dares you to complete maps using ONLY a hand picked team of monkeys. There are amazing rewards available, if you're up to the challenge!
~ Version 3.15 description
Challenge Monkey is a new event introduced since Version 3.15. It involves using only the selected towers to gain quadruple rewards. Unlike Preferred Monkey and the Bloons Monkey City event Monkey Teams, the only available towers are the selected towers, including no Agents either. All available towers and their upgrades are also 20% off.