Ender's training with the simulator

Ender trains extensively with the simulator, a device that simulates space battles. He learns to command fleets, using squadron leaders who are actually his friends from Battle School, including Alai, Bean, Petra, and Dink. The training becomes increasingly difficult, with Mazer programming the enemy to be more and more challenging. Ender is pushed to his limits, and he begins to suffer from exhaustion and stress. He has nightmares and starts to break down, but he continues to fight and win.