Godlike
Ryu, Nina, Bleu, Puka (Breath of Fire) vs. Lady (Shadow Hearts: FTNW)
Guv, Yangus, Jessica, Angelo (Dragon Quest VIII) vs. Vayne, Jessica, Niki, Flay, Pamela, Anna (Mana Khemia): MK parties only start out with the ability to support against crap randoms that they get the first overworld strike against. In a fight like this, somebody quick like Jessica gets the first turn while the support portraits are still gray. So magic burst wipes the vanguard and the replacements can't revive without items. Good luck to them from here on out.
Zidane, Garnet, Vivi, Steiner (Final Fantasy IX) vs. Zophar (Lunar: Eternal Blue Complete)
Heavy
Ryu, Rei, Momo (Breath of Fire III) vs. Yosuke, Chie, Yukiko, Teddie (Persona 4): Rei does something ineffectual, Ryu transforms while watching his teammates get swatted like gnats - too much good MT from the P4 guys, and Momo's slow IIRC. Ryu can't do shit with his limited OHKO damage that smacks into auto-endure and facing 2 revivers/fullhealers.
Ulrika, Chloe, Pepperoni, Goto, Enna (Mana Khemia 2) vs. Elyon (Breath of Fire: Dragon Quarter): Intent to Destroy and Dynamic Toss are pretty much the only things that pierce AD, and they do a piss poor job of it, and... Elyon's up shit creek anyway. Karma only kills 1 person a use, and the first people killed by it will be expendable crap like Goto and Chloe supporting for people who actually matter. Alter egos get put down hard by Enna, and Elyon's conventional attacks are just crap which get owned by healing reverb. While Ulrika's workshop eventually would run out of bodies, Elyon's mediocre HP can't stand up to all the little hits it takes for long enough. Oh yeah, not to mention that all attacks during a unite mode count as a single combo, so if any of those ever happens Elyon is SUPER fucked - AD just plain shuts off till it's over.
Sephiroth (Final Fantasy 7) vs. Alex, Nash, Mia, Jessica, Kyle, Nall (Lunar: Silver Star Story Complete)
Divine Weapon (Wild Arms 4) vs. Indalecio (Star Ocean 2)
Middle
Xorn (Grandia III) vs. Kefka (Final Fantasy 6)
Jecht (Final Fantasy X) vs. Hugo, Fubar, Sgt. Joe, Lilly (Suikoden III): MT 3HKO damage that delays a lot and doesn't miss is pretty hard for these guys to deal with. Jecht'll get an overdrive at some point, and triumphant grasp on Sgt. Joe after a delay-fueled double is the nail in the coffin. This gets worse if you don't allow yellow scarves, since now the duck has to keep SL on at all times to prevent "stone, stone, stone" and that means no healing.
Celes, Sabin, Edgar, Setzer (Final Fantasy 6) vs. Ramza, Agrias, Mustadio, Orlandu, Meliadoul (Final Fantasy Tactics): Mustadio's arm aim is turn 1 to me, so this is a slaughter. He incapacitates Edgar while Orlandu busts Celes's armor and Ramza carves her up. Sabin and Setzer, generously, can kill Orlandu, but then Melaidoul busts Edgar's armor and Ramza kills him, and agrias and mustadio are piling damage on Sabin, and then Ramza gets to join in on the party and there's all these random holy sword status chances flying around and yeah team FF6 is boned.
Lyn, Eliwood, Hector, Athos, Serra, Nils (Fire Emblem) vs. Lavos (Chrono Trigger): Athos is damn near capable of doing this alone. Buffs from Nils and healing from Serra would make it a slaughter, so Lavos has to kill them first while 4 strong FE characters beat his fucking face in. Um...
Light
Loki (Valkyrie Profile) vs. Daos (Lufia 2)
Luke, Guy, Tear, Jade (Tales of the Abyss) vs. Kuja (Final Fantasy IX): Counters + the "lol Tales healers" factor probably seals it.
Crono, Marle, Lucca (Chrono Trigger) vs. Pikachu, Charizard, Blastoise, Venusaur, Snorlax, Espeon (Pokemon)