Hmm, secondary characters/villains…
FF6: Perhaps Kefka, but he’s friggin’ nuts, might be better to use Gestahl; Rachel (Locke’s dead G/F); the Atma Beast, Daryl (Setzer’s girl).
FF7: Lots to name here… the Turks, Zangan (Tifa’s trainer), Don Corneo, Marlene, Dyne (Barret’s insane ex-friend), Professor Gast, Lucrecia, Shera (Cid Highwind’s girl) WEAPONs, Zack, virtually any of the Shinra staff, since none of them really died, per se.
FF8: Lots here too…Cid Kramer (B-Garden Headmaster), Martine (G-Garden Headmaster), Vinzer Deling, Ellone, Laguna/Ward/Kiros, Sorceress Adel, Julia Heartilly, Raine, General Caraway, Biggs/Wedge, Fujin/Raijin. I’d avoid Ultimecia if possible, because she just blows.
FFX: Yu Yevon, any of the Maesters, Braska, Yuna’s mother (never really was mentioned much, you could bring that into light, who knows). I guess Jecht wouldn’t exist, since technically without Sin, neither does Tidus, or Zanarkand for that matter.
FFX-2: Vegnagun, Shuyin, Lenne. Only played this game through once, that’s about all that sticks out in my mind except for the characters I mentioned earlier.
Hope that’s what you were looking for.