All of the games in the Commander Keen series are side-scrolling platform video games: the majority of the game features the player-controlled Commander Keen viewed from the side while moving on a two-dimensional plane. The player can move left and right and can jump; in every episode besides Keen Dreams they can also use a pogo stick to bounce continuously and jump higher than they can normally with the correct timing. The levels are composed of platforms on which Keen can stand, and some platforms allow Keen to jump up through them from below. Beginning with episode two, "The Earth Explodes", there are also moving platforms as well as switches which extend bridges over gaps in the floor. Keen Dreams and later games add fireman's poles that Keen can climb up or down, and with the exception of the 2001 Commander Keen also show the platforms viewed from slightly above so as to give a pseudo-3D effect. Throughout the series, once entered, the only way to exit a level is to reach the end, though for Keen Dreams and episodes four through six the player can save and return to the middle of a level, rather than only between levels like the other games. In between levels the player travels on a two-dimensional map, viewed from above; from the map the player can enter levels by approaching the entrance. Some levels are optional and can be bypassed, while others are secret and can only be reached by following specific procedures.
This article uses material from the Wikipedia article Commander Keen, https://en.wikipedia.org/wiki/Commander_Keen which is released under the Creative Commons Attribution-Share-Alike License 3.0, https://creativecommons.org/licenses/by-sa/3.0/.