Ys III: Wanderers from Ys
Release Year: 1989Departing the original Bump Combat formula, Ys III took a side-scrolling approach not unlike that of Zelda II. It was ultimately retconned by Ys: The Oath in Felghana.
Ys IV: Mask of the Sun
Ys IV: The Dawn of Ys
Release Year: 1993Developed by Hudsonsoft (who took some liberties with the story and mechanics), these two games technically took place between the original Ys II and Ys III stories. They were ultimately combined and retconned by Ys: Memories of Celceta.
Ys Strategy
Release Year: 2006Often regarded as the least popular game of the entire franchise, Ys Strategy (developed by Future Creates, not Falcom) was a somewhat misguided attempt at an Ys-themed strategy game for the Nintendo DS.
Oh, and that red-haired swordsman? That's not Adol Christin. That's Abel Renford, of course.
Ys vs. Trails in the Sky: Alternative Saga
Release Year: 2010This fighting game featuring characters from the Trails series and primarily Ys Seven was developed by Nihon Falcom for the PSP. An English release and remaster is expected this year.