Posted May 24th 2012
In the massive dark cavern containing a bridge, you normally meet 21 covies. But with a bit of effort that can actually be boosted to 35 by making 14 covies retreat there on foot from the two-Wraith area - including Shade gunners and Ghost and Wraith pilots once ejected, and even including the Banshee pilot after getting him down to the ground (though that may be hard without PAL Xbox). In the cavern itself, you can also trigger all covies on the near side (including the newcomers) to retreat across the bridge, to get the opposition into a more concentrated mob. Special extra work can boost enemy numbers by another 3 if you wish, making 38. As well as that you can bring along as many as 13 Marines to help you out, making for up to 52 personnel including yourself. Quite a party!
The battle doesn't have such extensive tactical possibilities as the other megabattles, but it's agreeably intense and kind of fun to set up too, so you should definitely give it a whirl. There's comprehensive set-up advice here, plus ideas for the actual battling. I'll also say that if you've never had the patience to set up a twin bridges megabattle with a large squad of Marines, this new one can give you some excellent big-squad battling for much less effort. It's also great for sniping and other long-range mischief.
In regard to the history, making covies move to the cavern was actually mentioned as early as September 2004 by Agony in a reply to one of my forum posts, though he talked of leading them there which isn't really how it works (I don't know if he realized that); so I'm certainly not the first to be battling an expanded horde of covies there. I suspect I ended up forgetting about that reply (found after writing most of this article) and latching onto the enemy retreat behaviour for myself a long time later, but I'm not sure. At any rate, a full exploration of the potential has been on my backlog of things to do for quite some while now, and finally I was prompted to get busy with it when PerseusSpartacus mentioned a cavern battling plan of his own, albeit with only the usual covies.