developers of Keen were unlikely to ever work together again on another game. On June 9, 2019 at Bethesda's E3 2019 conference for iOS and Android devices, a new game in the series was announced, again titled Commander Keen. Under development by ZeniMax Online Studios, the mobile game was announced to include tactical strategy elements and have both single-player and multiplayer gameplay, and star Keen's twin son and daughter, Billy and Billie. It was planned for release in the summer of 2019, but no release or further announcements were made, and all references to the game were removed from Bethesda and ZeniMax websites by June 2020. In addition to the initial releases of the games, several compilation releases have been published: the id Anthology compilation in 1996, which includes all seven episodes developed by id or Ideas from the Deep; a compilation release by Apogee in 1998 of the five episodes of Invasion of the Vorticons and Goodbye, Galaxy; and the 3D Realms Anthology in 2014, which also includes Vorticons and Galaxy. The Apogee-published episodes have also been released for modern computers through a DOS emulator, and sold through Steam since 2007 as the Commander Keen Complete Pack. Gameplay 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