Inspired by the intermissions in "Pac-Man" (1980) and bonus stages in "Rally-X" (1980), Yokoyama added a special bonus level. While planning, lead programmer Tetsu Ogawa informed him of a bug whereby enemies would simply fly off the screen instead of moving into formation. Ogawa expressed interest in incorporating the idea into the game, leading to the inclusion of the Challenging Stages. Enemies originally flew in one type of pattern, with more being added to increase replay value. Graphic designer Hiroshi Ono designed many of the sprites, including the player's ship and the Boss Galaga alien.