Godlike
Kaguya Nanbu (Super Robot Taisen OG Saga: Endless Frontier) v Lady (Shadow Hearts: From the New World): Just a gut vote, not thinking too hard about this one.
The Harlot (Shin Megami Tensei Nocturne) v Zophar (Lunar: Eternal Blue Complete): Harlot is an incredibly strong and hard to wall slugger/drainer but you can't overpower Zophar. You need some sort of cute gimmick to neutralize his magic completely and Harlot's just not that kind of dueler.
Arceus (Pokémon) v Tetri (Mana Khemia 2: Fall of Alchemy): Seismic toss oughtta be enough to OHKO through falling leaves, as those individual phases have very little HP (~30% PCHP by my estimation. Tetri relies A LOT on defenses). It certainly 2HKOs, which might also be enough since it's pretty likely that Arceus constantly doubles. Tetri is slooooow.
Ashera (Fire Emblem: Radiant Dawn) v Velius (Final Fantasy Tactics)
Lavos (Chrono Trigger) v Jade (Breath of Fire)
Teepo (Breath of Fire III) v Indalecio (Star Ocean: The Second Story)
Sora (Kingdom Hearts Series) v Lucia (Suikoden Series)
Heavy
Zapdos (Pokémon) v Rei (Breath of Fire III)
Princess Toadstool (Super Mario RPG: Legend of the Seven Stars) v Wugui (Shadow Hearts)
Arnaud (Wild ARMs 4) v Naoto Shirogane (Persona 4)
Middle
Florina (Fire Emblem: The Blazing Sword) v Luna Noa (Lunar: Silver Star Story Complete)
Enrique (Skies of Arcadia) v Stocke (Radiant Historia)
Shante (Arc the Lad II) v Dalton (Chrono Trigger)
Lich (Final Fantasy) v Virginia Maxwell (Wild ARMs 3)
Prier (La Pucelle: Tactics) v Espeon (Pokémon): I dunno about a 2HKO, but Growl and healing handle Prier pretty easily.
Bartholemew Fatima (Xenogears) v Tear Grants (Tales of the Abyss)
Sceptile (Pokémon) v Titania (Fire Emblem Series): No doubling for sceptile~
Light
Alenia (Suikoden V) v Nana (Grandia)
Euram (Suikoden V) v Big Joe (Xenogears)
Raja (Phantasy Star IV) v Nina Wyndia (Breath of Fire III): Raja's pretty good vs. light mages.
Banon (Final Fantasy VI) v Zhuzhen Liu (Shadow Hearts)
Mao (Shadow Hearts: From the New World) v Algus Sadalfas (Final Fantasy Tactics)