There are seven episodes of commander Keen. The first episode is called "Marooned on Mars", the second is called "The Earth Explodes", and the third is called "Keen Must Die". Those episodes made up the series "Invasion of the Vorticons". The fourth episode is called "The Secret of the Oracle" and the fifth episode is called The "Armageddon Machine". Those two episodes made up the series "Goodbye Galaxy". The sixth Episode is called Aliens Ate My Babysitter. It is a stand-alone episode. Commander Keen Dreams, the "lost episode" was made between the Keen 3 and Keen 4. It is the only Commander Keen episode that does not feature a pogo stick.