How do you play co-op mode in bloons td5?

To play co-op mode in Bloons TD 5, first, start the game and select the "Co-op" option from the main menu. You can either create a game or join an existing one by entering a friend's game code. Once in a game, you and your partner can choose towers, place them on the map, and work together to defeat waves of bloons. Communication and strategy are key to successfully managing resources and defending against increasingly difficult challenges.