Commander Keen in Goodbye, Galaxy!: The Armageddon Machine

You are eight-year-old Billy Blaze, boy genius to your neighborhood. Commander Keen to the rest of the universe. It's time to grab your trusty pogo stick and neural stunner, climb into the cockpit of your homemade Megarocket and blast off for the Shadowlands. To prevent the obliteration of life as we know it, you'll have to battle your way past deadly hazards and devious creatures, or end up as space toast.

Résumé

After completing the mission in episode one, Keen learns of the Shikadi's enormous ship, which doubles as the largest weapon ever built. So in episode two, titled "The Armageddon Machine", Keen faces his greatest challenge yet - to save the Galaxy!