"Praline and some creepy fans"
Praline (BD), Dehuai (SH), Garland (FF9) vs. Lenny, Naoto, Ultros: They probably kill Ultros before he gets a turn, which is real bad. Garland's not too durable but Praine/Dehuai are and can really grind non-healing teams down.
Praline (BD), Dehuai (SH), Garland (FF9) vs. Gilbert, Knight (FF1), Garan: Well, I don't think Dehuai + Garland can kill Gilbert before he gets a turn, so Gilbert does... bad things. He probably kills Garland and hurts at the others some. Knight + Garan may pile on and... potentially kill Praline if she was caught in the Deep Grudge, otherwise not. Kneejerk is this team can handle things from here, but I'm not certain since Garan is pretty bad, but the other team has no quick way to deal with petrify-immune knight.
Praline (BD), Dehuai (SH), Garland (FF9) vs. Kefka, Harle: Think so. Kefka wrecks the other team pretty fast.
Praline (BD), Dehuai (SH), Garland (FF9) vs. Van (TotA), Richard (S5), Flay, Miranda (G3): Really don't know. Pass for now.
I vote on Jenova-Death in general, who has 2HKO fire damage (or 4HKO MT), 60% silence, and nearly 2x average speed.
Team Boss Rush
Lassic, Marcello, Jenova vs. Lenny, Naoto, Ultros: Jenova can cook Ultros before he gets a turn.
Lassic, Marcello, Jenova vs. Gilbert, Knight (FF1), Garan: Marcello + Jenova can kill Gilbert before he gets a turn. The other two aren't winning a slugfest from there, not with how durable Lashiec is in particular.
Lassic, Marcello, Jenova vs. Kefka, Harle: I'm willing to buy them blitzing Kefka down before he gets a second turn.
Lassic, Marcello, Jenova vs. Van (TotA), Richard (S5), Flay, Miranda (G3): Yeah, this team is just overall good. AnotherGate is going to be brutal. Marcello and Jenova's best bet is probably to soften everyone but Van with their opening turns, then... even if the rest of the team blitzes, say, Jenova, a combination of AnotherGate and Marcello damage can probably drop Van and most of the rest of a team in an instant.
Team Boom
Jowy Atreides, Lyon, Geno vs. Lenny, Naoto, Ultros: Huge damage off good speed.
Jowy Atreides, Lyon, Geno vs. Gilbert, Knight (FF1), Garan: Geno Boosted Jowy easily kills Gilbert and at worst seriously injures Knight. Lyon finishes Knight. WATCH OUT KIDS, IT'S SOLO GARAN.
Jowy Atreides, Lyon, Geno vs. Kefka, Harle: Tough one. Kefka should probably kill Jowy, sure. Lyon + Geno still output sick damage, but not enough to kill Kefka (will kill Harle, though). Lyon will be boosted in the process, so Kefka probably can't OHKO her next (unless she triggers a counter... and those are 2/3, so maybe...). But Kefka needs to both a counter and to get a 50% doubleaction, I think, or a 3-2 on Lyon. Could happen, but kneejerk is no.
Jowy Atreides, Lyon, Geno vs. Van (TotA), Richard (S5), Flay, Miranda (G3): lol. Fastest person on enemy team is exactly the same speed as the slowest person on Team Boom. And he's not surviving unboosted Hungry Friend anyway.
Overpowered Pyro Team A 4-0
Overpowered Pyro Team B 4-0
Team Praline 1-2
Could be argued on some of these.