Origin
If you're curious, I was led to this megabattle back when exploring the business of horde boosting in the spiral path megabattle (see here for my January 2006 HBO forum post on that material). Specifically, it started when I was playing around with the underpass attack plan. When attacking from the entrance side, I realized that enemies were sometimes running off into the twin bridges area. Naturally I followed, and soon found that they'd chase me all over the place.
The first time I experienced this, I got a pretty extreme situation in which I was being chased by a gang of ten Elites. None of those pesky little fin-backed fellows or beaky freaks with day-glo dustbin lids; just ten of the big guys. Talk about scary. I'm afraid I wasn't quite prepared for it, and died horribly. On later occurrences, I had more of a mixture after me.
I was all set to include a mention of this novelty in the material on horde boosting, but then I found a way to tempt enemies through the underpass, giving masses of enemy in the next area. It was clear that this was a whole new megabattle in the making, so I decided to hold off on any mention until I got around to exploring it in depth; particularly the idea of arranging Marine support, which to begin with I wasn't even sure would be possible. Almost a year later, I've finally got around to doing that and realizing just how good the battling is, especially with a large squad of Marines. So now I'm wishing I'd done it sooner! Got a lot of spectacular battling to catch up with…