He programmed the first three Final Fantasy games,[3] the Famicom 3D System title Rad Racer, 3-D WorldRunner, and Secret of Mana.
[15] In October 1982, Arcade Express reviewed Zenith and scored it 9 out of 10, stating "celebrated Nasir proves his reputation" with "this visually striking first-person space piloting and shooting" game.
The programmers, especially Hironobu Sakaguchi (a long-time fan of Gebelli's work), were aware of Nasir's reputation and were excited to have him join.
[3] While at Square, Nasir programmed the game Tobidase Daisakusen for the Famicom Disk System, released in the United States in early 1987 as 3-D WorldRunner on the NES.
[19] His second Square project was Highway Star (Rad Racer in the U.S.), a stereoscopic 3-D racing game also designed for the Famicom 3D System in 1987.
[25] He went on to program Final Fantasy II, released in 1988, introducing an "emotional storyline, morally ambiguous characters, tragic events".
The game replaced traditional levels and experience points with a new activity-based progression system that required "gradual development of individual statistics through continuous actions of the same kind".
[22] Final Fantasy II also featured open-ended exploration[26] and an innovative dialogue system where players use keywords or phrases during conversations with non-player characters.
[28][29] Midway through the development of both Final Fantasy II and III, Gebelli returned to Sacramento, California from Japan due to an expired work visa.
The team who created the game had worked on the first three Final Fantasy titles: Gebelli, Koichi Ishii, and Hiromichi Tanaka.
In August 1998, Gebelli attended an Apple II Reunion in Dallas, Texas, at video game developer Ion Storm offices.
John Romero (Wolfenstein 3D, Doom, Quake) credited Gebelli as a significant influence on his career as a game designer.
[38] He also cited Gebelli as his favorite programmer and a notable inspiration, mentioning his fast action and 3D programming work on games such as Horizon V and Zenith.
[7] Jordan Mechner has also credited Gebelli's work on the Apple II as inspiration and as a major influence on the creation of Karateka and Prince of Persia.
Secret of Mana has also influenced later action RPGs,[36][43] including modern titles such as The Temple of Elemental Evil[44] and Dungeon Siege III.