Godlike:
Sulphur (PB) Vs Xorn (G3) - To add insult to injury, I don't see any reason why Sulphur's rocks o' invincibility should be disallowed (similar to letting FE bosses have the regen and defensive bonus from starting on a Throne), but even without 'em... Terminate likely OHKOs, and if it doesn't, Sulphur just does it twice. It's not like his durability is bad or anything, and Xorn needs a bit of time to get going.
Belial (WA4) vs Loki (VP1)
Heavy:
Cristo/Kiryl (DQ4) vs Erim (Lufia 2) - Sure, bad ID spam.
Elena (G2) vs Margulis (XS2) - Margulis is indeed pretty bad at full HP.... but he is fast and can build boost with his initial assault. Sure, Elena can buff a bunch during Margulis's suck phase, but Margulis has great HP to me (~3x PCHP?), so once she starts trying to kill Margulis there will be problems. Margulis with one Boost ready is barely a OHKO to average, but Margulis probably has time to grab two boost here and then blow Elena up in a boost-powered triple turn.
Odin (VP2) vs Fujin (FF8)
Light:
Melody Vilente (WA3) vs Tia (Lufia 2)
Aeris Gainsbourgh (FF7) vs Arietta (TotA) - Only played TotA Hard mode, so admittedly skewed perspectiv here, though I assume Normal mode has to majorly nerf Arietta to give Aeris a shot here.
Gares (OB) vs Renault (FE7) - Dodges his way to victory? It's been ages but I think Gares was back-row and used magic attacks too, so insert Resistance hype here, even if it does ignore counters. Ugh, at least Gares first form doesn't get held against Tarot Card spam, but it probably deserves to be held against one use or thereabouts.