High position defence
Associated movies… BCM222
Use a Banshee to drop yourself somewhere up high, to tackle the covies from there - or most of them anyway. The prime weapons for this are the sniper rifle and rocket launcher, but a pistol could also be good, and if you're low enough you might even try using plasma weapons. If you're in a viable position, a mini-challenge is to see if you can stop any enemies getting to the bottom of the spiral path.
On the Shade ledge
The easiest and quickest place to land is on the wide ledge holding the Shades. The enemy will have two different behaviours depending on where you're standing, and you can use this to engineer the type of battle you want.
If you're near enough to the underpass, the covies will advance as usual, heading down the spiral path and along towards the underpass. This is ideal if you want some long-range fun with the sniper rifle or whatever. I also enjoy lobbing grenades to the area of the rocks on the inside corner of the ice path. They bounce along quite a way, so it may take a few throws before you get your range right.
If you're further away from the underpass (in the left half or thereabouts, as you look out from the ledge), the covies will instead congregate on the spiral path, eyeballing you across the gap and also attacking any Marines down below. It can be quite a sight, particularly in regard to all the Jackals with plasma pistols overcharged, giving off that green glow. The Marines fight back, even trying to lob grenades up there, and this conflict is actually quite good fun just to watch! Enemies sometimes come over the edge due to clumsiness or evading grenades, giving the Marines something to tackle closer up, but they'll try to back off to return the spiral path. Enemies on the distant cliff often open fire too, aiming at the Marines as if the spiral path wasn't in the way. As a result, their shots often strike friendlies on the path. Hee hee! Anyway, when you've had enough of admiring the sights, you can have great fun sending rockets and grenades over to decimate the mob, as well as using other weapons of course.
On the underpass
The underpass offers three levels for a high defence. For starters there's the roof, adjoining the Shade ledge. Looking out from there, try the far left or far right for different views of the approaching enemy; but obviously the left corner will let you see them earliest when they come around the ice path. Higher up, you could drop yourself on the pinnacle with the three flashing red lights.
Lower down there's the 'pipe platform' sticking out the front, joining the two pillar-like pipes. You can jump down there from the roof or drop yourself off directly. It's not big mind. I'd say it's about the size of half a dozen Jackals, hammered flat into a tough leathery boarding then laminated to make a good firm platform. There's enough room to dodge around though, if any plasma balls come your way. It's a good spot for a bit of pistol marksmanship and you can safely jump down afterwards - or earlier if enemies start to get through your defence and you decide your Marines need help at closer quarters. I rather like this perch. You're closer to the action, and because you're lower down, enemies present a bit more of a target.
On higher ledges
Higher up than the Shade ledge is a narrow sloping ledge that runs all the way around the battle area. You can drop yourself off there but your Banshee is likely to slide off (never mind, we're just having fun). In a few places it's possible to survive the fall if you later attempt to jump down, but you'll need to land on a sloping surface to help break your fall. If you're far enough around towards the pass, your position will cause the Marines to advance up the spiral path, inevitably leading to conflict. You'll have a hard time keeping them alive, but it's great to watch!
Even further up in the mist there's another narrow ledge, and in some places this is wide enough and flat enough to properly land your Banshee. From way up here you won't have much chance of helping your Marines, but you can still enjoy long-range mischief. Very long-range mischief!
Incidentally, if you drop yourself off on a ledge somewhere up above the top of the spiral path, you can potentially see back into the pass which the covies came through. If you're up for some explosive fun, large groups of enemy standing around will make a nice target for your rocket launcher or grenades!
Bear in mind that it's possible to have spare weapons up on the Shade ledge or underpass roof or pipe platform; see my advice on getting spares up high in the Spare weapons section. As such, you could create a save dedicated to a high position defence plan.