Snow, reading over some of your votes, I'm not sure you always realise Xerneas's Geomancy has a charge turn? Maybe I'm misreading.
Xerneas (Pokemon) vs. Wendigo (FFX): Wendigo 2HKOs, and Horn Leech doesn't slow this down much. Geomancy's charge time screws it over here, the turn order goes (charge Geomancy), Wendigo, (Geomancy resolves), Wendigo. No way is Xerneas doubling before then.
Xerneas vs. Legretta (TotA): Yeah, I'd imagine Legretta bad full HP phase costs her this.
Xerneas vs. Fang (FF13): Xerneas can Misty Terrain then 2HKO with Moonblast, and yeah don't think Fang is doing much before then.
Xerneas vs. Scias (BoF4): Geomancy, Moonblast for a OHKO? This gives Scias two turns, and status could be bad... but yeah not really because Scias has to wake Xerneas up sooner or later. And Xerneas is faster at base (just edited BoF4 speeds into the stat thread).
Xerneas vs. Hiro (Lunar 2): Faster, Moonblasts twice.
Xerneas vs. Cristo/Kiryl (Dragon Quest 4): Cristo's ID certainly isn't worse than turn 2 here... but yeah it probably is turn 2, and Xerneas... actually has enough shots of Moonblast to effectively heal-lock with that, surprising.
Xerneas vs. Maxim (Lufia 2): Buffs up and smites.
Xerneas vs. Zapdos (Pokemon): Faster, 3HKOs first. Not sure I see how Xerneas is going to change this.
Xerneas vs. Sasarai (S3): Light Screen first, now Sas does 39% tops. This buys Xerneas time for Geomancy to weaken things further, and after that draining should easily outpace any Sasarai offence he still has left.
Xerneas vs. Say'ri (FEA): Kills in two attacks. Xerneas would, but evade. Not sure how Geomancy is supposed to help here, even if he then hits turn 1 he still needs three turns total, and if Xerneas barely 3-2's using a Geomancy strat against Land of Eternity it's not happening against average. Say'ri should do enough damage even if she stops doubling. (She doesn't to me.)
Xerneas vs. Amphysvena (XG): Shitty draining to the rescue! Ramsus damage so bad. That move should really be on Xerneas' default set.... although I guess everything there is useful.
Xerneas vs. Kain Highwind (FF4: TAY): Xerneas is faster and probably 2HKOs with Moonblast. Kain's healing even after Haste can't really meaningfully slow this down. It might ward off the initial 2HKO but longterm it's hopeless.
Denam (Tactics Ogre) vs. Wendigo (FFX): Denam is tough, such that Wendigo will need three turns to kill him. But yeah even if he Mighty Impacts every turn, that's not enough.
Denam vs. Legretta (TotA): 2HKOs once she activates her limit, and Denam damage not really good enough here.
Denam vs. Fang (FF13): Status.
Denam vs. Scias (BoF4): Hmm. Scias needs several shots, but his healing lets him control things pretty well.
Denam vs. Hiro (Lunar 2): Bang, you're dead.
Denam vs. Cristo/Kiryl (Dragon Quest 4): Thwack, you're dead.
Denam vs. Maxim (Lufia 2): Faster, tankier, and Maxim has problems getting IPs against those faster than him in general.
Denam vs. Zapdos (Pokemon): Wrong damage type for Denam.
Denam vs. Sasarai (S3): OHKOs.
Denam vs. Say'ri (FEA): They'll trade blows on the opening round and Denam should get enough TP for Mighty Impact on the second, which ignores counters and he may well get his second turn in before Say'ri's... and that would kill. Surprising. If Say'ri doesn't attack then Denam just sits there until he can Mighty Impact, so she has to. She can attack with something weaker, but Denam only needs to gain like 10 TP from damage received which means she can't really avoid it. EDIT: As per below, sword Denam loses... not sure which is better though, sticking with dagger for now.
Denam vs. Amphysvena (XG): Denam has no healing, so yeah.
Denam vs. Kain Highwind (FF4: TAY): Blink.
Rei (Breath of Fire 3) vs. Wendigo (FFX): OHKOs once beaten up.
Rei vs. Legretta (TotA): Rei can half fire, which means he won't be OHKOed... but still think this is a pretty bad setup for Rei.
Rei vs. Fang (FF13): I think. Pain will destroy Rei, so he pretty much needs to devote all his gear to blocking it, which means he can't block Slow or Deprotect.
Rei vs. Scias (BoF4): I guess Scias just 2HKOs?
Rei vs. Hiro (Lunar 2): Hiro definitely does.
Rei vs. Cristo/Kiryl (Dragon Quest 4): Rei goes Protectors + two Talismans, and lands Death first? Mmm... no, not at 34%. Still, he forces Kiryl to silence him, then goes Weretiger and gets in a free hit... at which point there's a heal-lock? Unless Kiryl can survive a normal + Uppered Weretiger hit? Upper is definitely potent... Kiryl cuts physicals by 9.5% before Upper and 82% after, so Rei does 77% with his two opening strikes. Kiryl... can just survive that.
Rei vs. Maxim (Lufia 2): Speed then blitz.
Rei vs. Zapdos (Pokemon): Don't see anything about lightning resist?
Rei vs. Sasarai (S3): Or earth.
Rei vs. Say'ri (FEA): Well Rei avoids being doubled, so his best bet is to go for Death probably, and hope that evade lets him live long enough? Hmm, no reason that shouldn't work.
Rei vs. Amphysvena (XG): Yeah, not blitzing this out.
Rei vs. Kain Highwind (FF4: TAY): Haste/Blink will wreck any offensive strategies, so Rei just goes for Death instead. He's faster but not ridiculously. Jump's charge time makes it trashy here, so that won't work... can't see Rei getting less than two Deaths off before Jump and one more after, or Kain goes for physicals and only 3HKOs, and I don't think even Haste lets Kain get in three attacks first? Mm, that's close. But... Rei has evade anyway, so yeah whatever.
Xerneas 9-3 (Pretty good. Not Godlike, I wouldn't think, but scary.)
Rei 3-9 (good anti-status stuff, speed, and Death. Back-ended damage is nice sometimes)
Denam 2-10 (Somewhat better than I expected, but not Heavy.)
