This version of Final Fantasy II is a revision that incorporates bug fixes and balance adjustments. The 'Rev 1' likely indicates a specific update to address issues present in earlier releases.  The modifications mentioned, like the 'Yang's HP Fix', point to direct alterations improving gameplay experience.  The core gameplay, story, and characters remain the same, but overall stability and some gameplay aspects have been improved. Square is the developer and publisher.

Final Fantasy II (USA) (Rev 1) [Bug Fix by Deathlike2 v1.0a] (Yang's HP Fix)

Final Fantasy - Mystic Quest (USA)