Go to Tall, Tall Mountain as Mario, Luigi, or Wario. Pick up the chimp at the top of the mountain. He will ask you to let him go. If you choose "No", you will be able to carry him wherever desired. The other monkey, however, will steal your hat and dodge you. You must catch him. After this, the monkey asks to be put down. The game forces you to do this. Next, bring the other monkey to the other one and place it down directly where the other one is located. Then pick both of them up. You will now be carrying two monkeys.