The Enemy Ace can only be killed on level 26. The Enemy Ace is very difficult to defeat because he flies by fast. Note: During his first flyby he will drop a bomb. Focus all fire on him to wear him down. Each time he takes some damage, he will create a shield. He will occasionally stop and spawn satellites to protect him while shooting a powerful canon. Once again, focus on him by moving from side to side, shooting a few satellites (or use a bomb), and wear him down. He will create fewer satellites each time. You only have a very limited time to kill him. If needed, quickly quit the game to avoid advancing to the next level.