Super Mario Bros. was originally planned to have an "air, land, and sea" concept. While the player normally runs on solid ground and swims underwater in certain levels, designer Takashi Tezuka explained in interviews that Mario would have been able to fight in the air while riding in a cloud. Instead of creating more brand new air-based enemies, they attached wings to an existing enemy to save on memory, resulting in the creation of the Koopa Paratroopa. However, the trial demo created to test these levels was deemed not fun to play, feeling more like a shoot 'em up game than what they were hoping. On top of this, the levels were deemed to be contributing to the memory constraints, leading to their removal. However, Tezuka strongly felt the game should still have air-based levels, leading him to suggest an idea to director Shigeru Miyamoto inspired by the fairy tale "Jack and the Beanstalk", where Mario could climb a vine from a Question Mark Block into the clouds, allowing players to collect coins in certain levels. Miyamoto liked the idea, and subsequently created the vines and constructed the game's bonus areas from existing elements. The "air, land, and sea" concept and Mario's ability to fight while in the air or clouds would be added in subsequent games in the series.