Godlike:
Emelious de Pamela (G3) vs Melc Crystals (G3): For sake of argument I'm going to take these two exactly how they appear in game, multiple parts and all. Emelious can probably one-round one of the golem's arms, though not the body. Melc Crystals will respond with Hellmixer + Hellburner. This... is probably enough to kill the sword, but not Emelious himself. Sword's probably worth killing, it does so much damage. So yeah, that. Emelious goes again, possibly getting two turns with his body now... but with the lower damage, even with some MT from the first form, I don't think he can kill a second arm. So yeah the damage repeats and Emelious' next turn will be even worse, kill one arm or main body... but I think he still barely dies regardless. It is close. To make matters worse I'm certainly more inclined to hold Emelious to one part than Melc, and that completely screws him over if so, because Hellmixer becomes that much more potent.
For Dhyer, damage absolutely does rise a fair bit between Melc Crystals and Emelious (the stat topic entries say 2300 -> 4000, which is certainly possible). There are two very long dungeons between them (probably around 25% of the game), and with the eggs you get in the first one, there is a very good chance you gain some high-level spells between them too, as well as Ulf's more damaging techs.
Alternis Dim (BD) vs Jenna Angel (DDS): Uh Alternis very easily survives one shot of Jenna bullshit. Two is debatable. However I don't care much for HP buffering.
Lady (SH3) vs Lavos (CT): Yeah probably.
Nobutsuna Kamiizumi (BD) vs Ryu (BoF3): For Snowfire, Kaiser Ryu "cuts physicals by 222" in a game where average HP is 224. This is actually very far beyond two-shield knight in defence, who "only" cuts physical by 1.5x what is needed to null average. You do not kill Ryu with defence-subject physicals, and Kamiizumi's Atk, while good, isn't -that- exceptional anyway (most of his overkill comes from the multiplier on his counters which is a multiplier AFTER defence).
High Heavy:
Black Mage (BD) vs Wren (PS4): Sigh.
Jowy Atreides (S2) vs Odd Eye (SF2): Jowy's defence really isn't that special, mostly offsets his HP. So Odd Eye should one-round. Does Hungry Friend OHKO first? Do I have any clue how I see Odd Eye HP these days? what is support credit how do I uguu.
Lucina (FE13) vs Shania (SH3): Shania should tank a Lucina turn. After that she uses Sanlittobell, which gives her 166% speed and thus the next turn, which she uses to heal. Lucina's now up against someone who cuts physicals by 63%, I don't think any amount of Aether hype is letting her OHKO ever again. (Also if you're the type to let speed buffs affect such things, Lucina just stopped doubling.) So yeah, Lucina is totally fucked if Shania gets a turn. You could certainly hype Aether giving her the one-round, but I'm not inclined to respect it that much myself. If you want to play the odds, Shania has a pretty good chance to go first here which should probably offset Aether chances.
Raquel Applegate (WA4) vs Citan Uzuki (XG): Tide analysis covers the day, I see no flaws here. I use a non-Kokei damage average, which helps Citan a bit, but shouldn't make the difference, especially since I probably also deny Citan the small atk boost of his final sword which has literally zero in-game use.
Low Heavy:
Croco (SMRPG) vs Demi (PS4): Uh, very much opposite ends of this division.
Fujin (FF8) vs Sofia (DQ4): Surely faster, lands some status or other, or just HP-locks with Sai.
Sharon (LoL2) vs Sceptile (PKMN): Sceptile is faster. If he 2HKOs, he just wins, and without knowing how good Legaia 2 MDef is this is hard to say. But... if he only 3HKOs, let's take a look at what happens. He'll go first, and needs to dodge a limit since Sharon will use her first turn to get to 100 AP. Of course, Sharon's own damage isn't very good, and she risks running right into Overgrow which would allow the 2HKO to occur. Granted, Sceptile's draining will trigger the limit after two uses, so he can't play around with that as well as usual to ensure he sees a limit of his own, and Sharon is fast enough that he can't go crazy with doubleturns like he often can. I do think the fight favours Sharon if Sceptile doesn't 2HKO... but there's a pretty good chance he does (47.5% to average) and Sceptile's odds are a hell of a lot better if that judgement call goes against him than vice versa, which makes me favour him.
Mia (FEs) vs Elly van Houten (XG): Well, the form with functional Vantage should take this, despite being worse overall? Or is it? Wonder how often this sort of thing comes up. Abstain for now...
Middle:
Raynie (RH) vs Brad Evans (WA2): Not sure how I feel about RH sleep, or more generally about switch. But... probably.
Tifa Lockheart (FF7) vs Flay Gunnar (MK1): Tifa needs a L2 limit, and Flay can dodge that. Timed cards are bad here, but buff, Big Impact, Screwdriver works.
Virion (FE13) vs Rena Lanford (SO2): Sorta confused by the Virion votes? If he 2HKOs it's baaarely, and Fairy Heal is dirt cheap (35 shots), easily outlasting a brave weapon as noted (and Virion can't possibly heal-lock with anything else). Protection probably wards off the 2HKO to boot. Killer crits scare nothing, half of a Brave weapon at base yeah whatever.
Nowi (FE13) vs Mario (SMRPG): Don't see why Mario wouldn't be counterable, he's all ST (or focused stuff, yeah not hyping that as avoiding counters).
Shame:
Liz (WA2) vs Castform (PKMN): Liz is like half PCHP, but he can 2HKO Castform with bombs, and goes first. So... does one Castform turn + two self-damages kill Liz? Yeah, no. Should note that by the listed HP in the stat topic, Liz will miss the 2HKO, but I see those figures as too high (twinked for max HP Plus is too much for me, since you can permanently miss said boosts).
Guido (G1) vs Nina (BoF3): Thank goodness, Guido gets someone competent.
Igganova (PS4) vs Guard Scorpion (FF7): TAIL LASER is MT, and there's no way in hell I don't see Igglanova's spawns falling for "attack when the tail is up!"