By the end of 1980, an Apple II version of ZorkI was completed and sold through Personal Software. Infocom began receiving requests for hints and maps as predicted, and Berez began handling map and poster orders while Dornbrook wrote customized hints for players; in September 1981 he founded the Zork Users Group as a separate company to handle all mail order sales and hint requests. Infocom eventually produced hint booklets with progressive answers to questions written in invisible ink, branded as InvisiClues. Meanwhile, Lebling worked on converting the second half of Zork into ZorkII, but in the process thought up several new puzzles for the game. Although as late as December 1980 he told Byte that it would be a two-part game, it soon became clear that the second half would not fit into the allotted space. As a result, the game was split again into ZorkII: The Wizard of Frobozz and ZorkIII: The Dungeon Master. According to Lebling, splitting the game into episodes led to different atmospheres: ZorkI was focused on exploration and Adventure-style gameplay, II had more of a focus on plot and added magic spells to the base game, and III was less straightforward, with time-sensitive aspects. Marc Blank constructed ZorkIII and added gameplay changes such as the modified point system to move the game away from straightforward dungeon exploration.
By the end of 1980, an Apple II version of ZorkI was completed and sold through Personal Software. Infocom began receiving requests for hints and maps as predicted, and Berez began handling map and poster orders while Dornbrook wrote customized hints for players; in September 1981 he founded the Zork Users Group as a separate company to handle all mail order sales and hint requests. Infocom eventually produced hint booklets with progressive answers to questions written in invisible ink, branded as InvisiClues. Meanwhile, Lebling worked on converting the second half of Zork into ZorkII, but in the process thought up several new puzzles for the game. Although as late as December 1980 he told Byte that it would be a two-part game, it soon became clear that the second half would not fit into the allotted space. As a result, the game was split again into ZorkII: The Wizard of Frobozz and ZorkIII: The Dungeon Master. According to Lebling, splitting the game into episodes led to different atmospheres: ZorkI was focused on exploration and Adventure-style gameplay, II had more of a focus on plot and added magic spells to the base game, and III was less straightforward, with time-sensitive aspects. Marc Blank constructed ZorkIII and added gameplay changes such as the modified point system to move the game away from straightforward dungeon exploration.