Commander Keen 4: Secret of the Oracle

Commander Keen 4: Secret of the Oracle is a platform game, the fourth in the Commander Keen series as a whole, and the first in the second series Goodbye, Galaxy.

Eight-year-old genius Billy 'Commander Keen' Blaze receives an interstellar transmission while working on a Photachyon Transceiver (a radio that can receive signals anywhere in the galaxy). While the transmission is choppy, Billy manages to figure out that the galaxy is once again in danger from an alien race known as Shikadi. In order to get more information about this threat, he sets out to consult the Oracle. But it turns out that the eight Council Members necessary for the Oracle's activation have been kidnapped by the Shikadi and imprisoned in the dangerous Shadowlands. Billy heads out to save the Council Members.

The game begins with a top-down map of the Shadowlands. This is the level select screen, where Billy can walk around and the player can choose the next level they want to enter (though some of the levels are islands located on a lake and require you to find a wetsuit if you want to reach them). On each level, Billy has to make his way to the exit. Once a level is completed, Billy ends up back on the overhead map.

The levels are typically full of enemy creatures, such as poison slugs, deadly mosquitoes or hopping crazy mushrooms. There are also many hazards - pits, cannons, spears. If Billy gets shot or touched by an enemy, or falls into a pit or touches something hazardous, he dies and loses one life.

Thankfully, Keen can stun most enemies with his raygun, although some cannot be stunned at all, and some are only stunned for a few seconds. Keen also carries a pogo stick which allows him to jump very high. Other items to find include: ammo, gems that acts as keys to open locked doors, bonus items which give score, raindrops (100 raindrops give extra life) and the rare Lifewater Flask which gives an extra life.

Id Software did not produce any more games in the Commander Keen series after Goodbye Galaxy besides the co-developed Aliens Ate My Babysitter. Another trilogy of episodes, titled The Universe Is Toast, was planned for December 1992, but was cancelled after the success of id's Wolfenstein 3D and development focus on Doom. When GT Interactive wanted to publish Doom II, it proved itself to id by quickly selling 30,000 copies of Goodbye Galaxy. A final Keen game, Commander Keen, was developed for the Game Boy Color in 2001 by David A. Palmer Productions in association with id Software, and published by Activision. Goodbye Galaxy has been released as part of several collections since its first release: the id Anthology compilation in 1996, a compilation release by Apogee in 1998 of Invasion of the Vorticons and Goodbye, Galaxy, a similar compilation in 2001 by 3D Realms titled Commander Keen Combo CD, and the 3D Realms Anthology in 2014. They have also been released for modern computers through a DOS emulator, and sold through Steam since 2007 as a part of the Commander Keen Complete Pack. According to Steam Spy, as of June 2016 approximately 200,000 copies have been sold through Steam.