I can defeat the JLA. 🙂
Here's how:
The Green Lantern: This one's so simple -- I just catch him not actively using his ring and snipe him. As a backup (in case I should miss or otherwise somehow fail to kill him outright), I'll take a page from Batman's book (but in a different way) and carry at LEAST one flash grenade, as well as a backup close-range weapon -- probably an SMG with decent accuracy, like a slow-fire M11. After all, as we all know, a blinded Kyle is a nigh-helpless Kyle. 😉
I now have a Green Lantern ring.
Martian Manhunter: Hell, I have a Green Lantern ring! But I want to save power on it, so I bring along a flamethrower, an SMG loaded with incendiary rounds, and a phosphorous grenade or five. Burn baby burn ...
The JLA is now cut off communication-wise.
Batman: Pathetically simple. I just turn on the Bat-signal and wait for him. Hi, Batman! I have a Green Lantern ring, and you do not. Bye, Batman! Since that took essentially no time to accomplish, I haven't burned an appreciable amount of power. Acceptable.
Wonder Woman: For this one, I open with smoke grenades (having already donned night-vision goggles based on thermal imaging so I can track her heat signature) and then unload with my .5 Inch Heavy Machine Gun. It's already been demonstrated that a high-powered rifle can give Wonder Woman a concussion ... so repeated pummeling from a weapon of this calibre should feel to her like being pounded on by Lennox Lewis would feel to me. And blinded by the smoke, she can't block effectively. 😉 Should all else fail, I fall back on the power ring. But I don't want to rely on that.
The Flash: Oh, this one's hard. This one's really hard. Theoretically, I could kill him by just sniping him, but it would depend on who was writing him that day. He can either be blindsided easily or can react to a bullet the instant it touches his skin, even when he didn't see it coming. Who can tell? 😛 So I try to snipe him. If I fail, he'll race up to me no doubt, but I've already shielded myself using my ring. So now I'll trap him in a bubble, and now he's the fastest man alive who can't move. And now I'll shrink the bubble ...
Superman: Assuming Superman's existence also implies the existence of kryptonite, I have it made. Infinite resources and prep-time means I WILL have some of this on hand, and then on top of that, I have the ring. No way he can handle both at the same time. 😉
Aquaman: I'm not letting him get anywhere NEAR me with his telepathy. Once again, sniping with a high-powered rifle is all that's needed. His durability is superhuman, but it's not THAT superhuman.
Plastic Man: Actually, I think Batman had the right idea with this one: freeze and shatter. After that, I take the individual pieces and spread them far and wide. And incinerate them, if I can. Or use the ring to fly some of them out into space ...