Godlike
Heat (Digital Devil Saga) vs Marisa Kirasame (Labyrinth of Touhou) - Tanks a Master Spark with Tentacles and that's all Marisa can do.
Lamington (Disgaea: Hour of Darkness) vs Ronin (Etrian Odyssey Nexus) - The durability and status resistances kinda spoil Ronin's tricks
Riou (Suikoden II) vs Ezel Granada (Super Robot Wars OG Saga: Endless Frontier)
Yuna (Final Fantasy X) vs Satanail (Star Ocean: The Last Hope) - Aeon Parade does its thing, but it's close enough that it could go either way. Faize having 4 meatshields of his own makes it questionable if Yuna takes this if you don't allow the optional Aeons, and obviously Aeonless doesn't stand a chance...
Heavy
Mei-ling (SaGa Frontier) vs Tim (Brigandine: Legend of Runersia)
Mystic Knight (Final Fantasy V) vs Harbinger (Etrian Odyssey Nexus)
Olberic Eisenberg (Octopath Traveler) vs Temenos Mistral(Octopath Traveler II) - Cute. Looks like Temenos can 2HKO, while Olberic 3HKOs... Olberic does go first, so he may be able to boost and 2HKO, but he just misses it by the damage average I was using.
Kyra Tierney (Phantasy Star IV) vs Xander (Fire Emblem Fates) - Xander tinks off of Kyra's def-buffing game.
Middle
Empoleon (Pokémon) vs Minorio Aki (Labyrinth of Touhou 2) - Minoriko outspeeds and buffs her res to the point that Empoleon's special attacks don't do anything. Empoleon has to buff with Swords Dance or just try to whittle down Minoriko with pitiful Drill Peck damage... while Minoriko still easily 3HKOs.
Mallow (Super Mario RPG) vs Createur Rosenqueen (Rhapsody II: Ballad of the Little Princess) - Assuming you allow Crea her unique monster summons, she's got a full suite of turn 1-2 status ailments and enough magic resistance that Mallow isn't 2HKOing
Peter (Shining Force II) vs Rinkah (Fire Emblem Fates) - Kneejerk Peter respect
Yukiko Amagi (Persona 4) vs Divine Punisher Shaman (Etrian Odyssey V)
Light
Thief (Final Fantasy V) vs Corselia (Suikoden Tactics) - Thief goes first and eventually doubles, but I think Corselia 4HKOs Thief's pitiful MDur after she lays down Water tiles. Not sure, especially since she only has 3 shots of her attack magic and then has to finish up with staff whacks.
Nanami (Valkyrie Profile) vs Amalia (Chained Echoes) - Surely Amalia beats a VP1 Mage?
Primrose Azelhart (Octopath Traveler) vs Seraphina (Disgaea 5) - Allowing Primrose her Allure Summon she can 3-round Sera. Sera's Evade is good enough to make that 4 rounds. Sera 5HKOs average, but Primrose's durability is trash, so it's probably a 4HKO. But Primrose goes first. Maybe Sera's Counters or not allowing Allure would swing this?
Umaro (Final Fantasy VI) vs Ivy (Fire Emblem Engage) - Kneejerk anti-Umaro vote