Chu-Chu: 24% magic damage (8 MP), or 21% (4 MP), 70% healing (2 MP), 64 MP, 74% speed, 1.44/0.75 mdur. Takes a large pdur hit to block status (pdur becomes 0.78).
Chu-Chu vs. Rennac (Fire Emblem 8): Rennac 3RKOs, Chu-Chu can heal and toss in damage to kill in ~5 attacks considering evade. Rennac does ATB-double periodically, but even so, I don't think Chu-Chu runs out of MP. Rennac's killer damage is terrible especially against high subtractive defence like Chu-Chu, don't feel like hyping that. EDIT: Or he steals her accessory, since I forgot he can do that. That gives him a 2RKO and a win.
Chu-Chu vs. Luna (Lunar SSSC): Chu-Chu blocks sleep or gets wrecked. With sleep blocked, Chu-Chu... still barely avoids a 2HKO from buffed Luna. Still, Luna 3HKOs and Chu-Chu 5-6HKOs depending on damage used... Chu-Chu does have better healing relatively, but it's not enough, especially since Luna's offence isn't burning her own MP, so Chu-Chu runs out first.
Chu-Chu vs. Thomas (Suikoden 3): Thomas only 6HKOs while Chu-Chu at least 4HKOs, Chu-Chu can heal at safe times to ward off any threat of stun.
Chu-Chu vs. Selphie (Final Fantasy 8): Probably. Chu-Chu's bad speed gives Selphie a wide limit range even if Chu-Chu comes up with the perfect chip strategy.
Chu-Chu vs. Marivel (Wild Arms 2): Guillotine.
Chu-Chu vs. Dragoon (Final Fantasy 5): Jump is useless, but maybe MP stealing...? Entirely comes down to that. Chu-Chu once out of MP is utterly awful. And... honestly, yeah, I'm not sure exactly how effective I see that being, but it doesn't need to be great to run Chu-Chu out of MP before she kills here.
Chu-Chu vs. Primrose (Octopath Traveler): Kills on turn 3 with her max-buffed damage. Chu-Chu isn't stopping that.
Chu-Chu vs. Nina (Breath of Fire 3): Like Dragoon, I think MP draining is the only hope here for Nina. Unlike Dragoon the MP drain is blocked by status protection in-game and Chu-Chu has no reason not to load up on that against Nina's lack of physical.
Chu-Chu vs. Female Thief (Final Fantasy Tactics): Stealing the armour should yield a 3HKO thereafter (the armour is like a 1.16 increase in pdur raw according to my notes, losing that nearly triples the damage Chu-Chu takes), which should enough considering the turnsplit. This feels like a rare fight where stealing is decisive, due to the unique combination of Thief facing a tanky healer with damage/speed too bad to threaten Thief before the steal can go off.
Chu-Chu vs. Rufus (Final Fantasy 7): Chu-Chu pretty good against bland Light physicals.
Chu-Chu vs. Jelanda (Valkyrie Profile): Jelanda's only hope is to run Chu-Chu out of MP with her own healing. And that... actually should happen? Jelanda heals every 4 turns, Chu-Chu gets 3 turns during that which isn't enough to do 80% to Jelanda. Wow.
Gilliam has 0.95/0.89 durability, just above average turn 1 speed, 23% damage (also melee counter), regen (4 turns of 10%, 40 MP), and 36% healing (65 MP), 319 MP total. 4x Heal + 1x Loop Heal typically.
Gilliam vs. Rennac (Fire Emblem 8): Gilliam opens with Loop Heal, Rennac does 53% - 10% from regen - 36% from healing = net 7% per turn until Loop Heal wears off, then net 17%... kills on turn 6 after Gilliam doesn't heal. Gilliam will spend five turns on spells then one finishing attack, meaning he gets five counters and one attack for six attacks total. He... 4HKOs, but due to his bad accuracy, Rennac has around 44% evade. If Rennac dodges 3 times he wins, which is... probably just over 50%. Plus Rennac might crit (Gillliam might crit too, but Rennac's crits are way more potent). Close!
Gilliam vs. Luna (Lunar SSSC): Way deeper resources. Also better damage and durability after she buffs.
Gilliam vs. Thomas (Suikoden 3): Gilliam only hits Thomas with one attack out of six. Granted, he does 4HKO, but needing ~24 attacks to win... hard to imagine that cuts it, even with counters in there. Assuming uses five turns on heals, he's killing sometime around turn 15, and 15 turns of Thomas offence kills Gilliam no matter how much he heals.
Gilliam vs. Selphie (Final Fantasy 8): Selphie gets a good limit, part 2.
Gilliam vs. Marivel (Wild Arms 2): Guillotine.
Gilliam vs. Dragoon (Final Fantasy 5): As with Chu-Chu, the MP busting is decisive.
Gilliam vs. Primrose (Octopath Traveler): On top of Gilliam's other problems, he's at least somewhat weak to dark here.
Gilliam vs. Nina (Breath of Fire 3): Gilliam 3HKOs, but with shaky accuracy (Nina probably dodges once), so 4HKO. Nina... probably just spell barrages him to death first? I'm not sure exactly what average I use but Nina 3HKOing seems reasonable to me, and he runs out of MP first if he tries to stall her.
Gilliam vs. Female Thief (Final Fantasy Tactics): Steal Heart makes him heal and buff her, once he's out of MP she can probably win the resulting slugfest though it's sadly close due to his counters.
Gilliam vs. Rufus (Final Fantasy 7): Rufus is not good.
Gilliam vs. Jelanda (Valkyrie Profile): Gilliam does at least 4HKO Jelanda to overpower Heal. So can she just beat him in a slugfest? No, probably not. Jelanda evade sucks, Gilliam probably does hit four times in a row.
Flayn is doubled by average (though if unweighed, not by much). Frozen Lance does 35%, Excalibur does 29%, Fire does 23%, Nosferatu does 17% (-5% on counters for the spells, Frozen Lance doesn't counter). 12 uses of Nosferatu, which also heals 26%/19%, Flayn herself heals 50% at base. 0.62/1.93 durability, capped Charm.
Flayn vs. Rennac (Fire Emblem 8): Rennac does 81%, not good enough since Flayn counters, until she whiffs Nosferatu at least... which does happen pretty fast? But actually, Flayn afford that. Rennac could go for crits though... and with Flayn's awful luck, I'm inclined to actually respect that enough to win here.
Flayn vs. Luna (Lunar SSSC): If Flayn ever equips anything that weighs her down, she gets doubled... so Luna puts her to sleep then wakes her up with some monster damage. And I think Flayn probably needs Nosferatu to not get beaten down here.
Flayn vs. Thomas (Suikoden 3): Thomas does 91%, which... sounds good but actually doesn't let him win barring a Nosferatu whiff (which I'm not inclined to buy against someone without MEvade) or Thomas crit (not hyping that, though Flayn's luck means it's not crazy).
Flayn vs. Selphie (Final Fantasy 8): Selphie has almost the same damage as Thomas, so the match plays out similarly. I think Frozen Lance as a finisher means Selphie isn't going to get a limit.
Flayn vs. Marivel (Wild Arms 2): Don't think her status is worth much here.
Flayn vs. Dragoon (Final Fantasy 5): Flayn's ability to deal with all these low-damage fighters is kinda impressive? Loses if you see Jump doubling, I don't.
Flayn vs. Primrose (Octopath Traveler): Don't try to win with magic damage against Flayn in Light.
Flayn vs. Nina (Breath of Fire 3): Ayup.
Flayn vs. Female Thief (Final Fantasy Tactics): Caduceus is immune to being stolen in-game, funny. Charm's interesting but doesn't get around the core regen problem.
Flayn vs. Rufus (Final Fantasy 7)
Flayn vs. Jelanda (Valkyrie Profile): Flayn can 4HKO to overcome Jelanda's own Heal, preventing this from being the longest match of all time.
Flayn 9-2
Chu-Chu 3-8
Gilliam 2-9
There's definitely a level of physical damage where Flayn just starts dying horribly even in Light (it's just above Thomas), but this field didn't have much of it. So I don't think she's quite as good as this field made her look... but still, exceeded my expectations for sure. Gilliam is terrible.