Hmmm... my first thought was "Legato!" but at a second glance I had my doubts.
While he can force everyone to kill each other, he's been shown to be overwhelmed by creatures of great power, like Vash. Perhaps he would be unable to control so many powerful creatures at once. Though honestly he's lethal smart and reaaaally devious, so he'd probably find a way to cut everyone off one by one till none was left.
But that's only if you don't count Elendira. Honestly, she's a freaking BAMF.
Not once did Legato ever attempt to control Elendira, even when she threw drinks at him or insulted him. Either that means he could not control her successfully, or knew that if he tried she'd instantly kill him. (Or they had a weird mutual hateful relationship in which they got off on each other's verbal abuse and competition over their devotion to Knives, which thus kept them from killing each other... which is my head canon, but I'm keeping that to myself!)
I'd say Livio also has a pretty damn good chance of winning, but only if he and Razlo work together as they did to defeat Elendira at the end of Trigun Maximum. Though, again, if Legato's got any sway here, Livio would likely be his first target to use to mow down the rest of the competition.
But, since you said no Eye of Michaelor Elendira, I'd go with Legato all the way. The rest of the Gung Ho Guns are good but their skills and tricks fall apart the moment you mess with their heads.
But let's say Legato's out of the picture too, cuz he's broken:
Monev the Gale is destructive but a few well-placed bullets will down him. Plus, he's afraid of dying and honestly only fights to be free. He'd put up a good fight but he's only human.
E. G. Mine.... just... no. Assume he's dead within the first millisecond, lol.
Dominique might stand a chance, given her hypnotic abilities, but break through that and she'd go down like hot butter. Honestly, just keep your eyes shut and shoot everywhere and you'll get her eventually.
Leonof might stand a good chance, as long as he has spaces to hide in. If it's an open area, a well-placed shot would down him.
Hoppered also stands a good chance if he just destroys stuff at the get go. But against a whole lot of people, he'd constantly be vulnerable because his back would always be against someone.
If Midvalley can get a breath in immediately starting the battle, he'd probably be able to debilitate the vast majority of his opponents. But if he can't get everyone in one go, another well-placed bullet would off him.
Grey the Ninelives might be able to plast quite a bit too but against Midvalley I feel like all nine of them would fall swiftly, unless their armour blocks sound in which case they'd likely be of the stronger bunch.
Rai-Dei is fast and accurate but I don't feel like he'd live very long, lol.
Though, honestly, if Zazie has access to the rest of the sand worms then he'd probably win. But if it's just him, he's easily fucked
Sooooooo.... if no Legato, Wolfwood, Livio or Elendira:
Zazie would win if sand worms are available, otherwise, I'd say Midvalley could win if he acts faster than everyone else, else, Grey the Ninelives would win.
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