Sierra 117 2.0
Sniper Alley! As the name suggests, you are about to hate the African Jungles very much. A few tips before we get started. The first is to realize that the forest contains both Marksmen and Snipers. Several of each are lurking in the trees, and their spawns may vary. For now, assume all Jackals are Snipers since they can one-shot you every time. Better to be safe than sorry. Also, a blue light means they know you're there. If they're shooting in your direction, jump back into cover for a few seconds and wait for them to lose interest before attempting to shoot back.
When you reach the small tree near the back, hold up. Usually a Marksman parks himself either up in the tree or just at the base. Behind him, at least two more Marksmen will be in position. One usually hangs out on a rock to the left, while the other stations himself further up on the right. The whopper, though, is the Sniper keenly hidden on a rock high up on the left that's hard to see due to the sunlight. That guy is your biggest threat as shown in the above video.
It's time, now, to focus on the enemies on the left edge of the U; usually one or two captains and a few Grunts. Use the Carbine for the Grunts, then backtrack and grab a Beam Rifle for the Brutes. This area is a bit tight for safely pulling off any trick shots, but fortunately roughly 3 shots from the Beam Rifle will kill their armor, leaving them vulnerable to headshots. When you've killed as many foes as you can from your current vantage point, again fill up on ammo, grab your Carbine and BR, and jump down.
I consider this area to be one of the most hear-pounding sections of the mission. You're in a strict, confined area of space with little place to hide and enemies coming at you from nearly every direction, usually from up above. First thing's first. kill the enemies that are already in place on the ground. A cluster of Grunts will usually be chilling around the Phantom, so pop out, take a few shots with your Carbine, and duck back into cover. Rinse and repeat until the Grunts are either dead, or the survivors have retreated to an area just out of view. If there are any Brute Captains remaining, make use of any Plasma Pistols you see laying on the ground, and do the ol' combo-kill to dispose of them.
This will be your main combat zone from here until the Dam. You can safely range shoot the Brutes, and are also far enough away from the mainland that you have plenty of time to see Grunts and Jackals approaching from afar. This is the safest place to be at this point. Stock up on BR ammo and wait for the enemy to approach. Arbiter will often times join in on the fun by charging the area just up the hill near the bridge. Let him. Back him up by popping any Grunts you see. Often times, he'll deal with the Jackals himself. Whatever's left can be dealt with via any grenades you happen to be carrying or by simple plasma-punching. You can either choose to range-shoot the Brutes, or get close up and combo-kill them. At this point, it'll come down to what you feel most comfortable with doing.
Before heading off to the Dam, make sure your Battle Rifle is fully loaded, and grab a couple of Plasma Pistols too. Things are about to get messy...
As soon as the cutscene ends, head down through the cave and rush the lower level of the bridge. The biggest risk you'll be facing on your way down come from the two Snipers located on the other side of the dam, but once you're underneath, they shouldn't be a problem for you. At this point, you'll need to get behind on of the section columns and poke your head out from time to time in both directions. At some point, usually a few Grunts from either way will be hobbling down there after you, so ready that Battle Rifle. If they start throwing grenades, just back into cover. They usually overshoot their target anyway, so they should be a good distance from you when they detonate. If the Chieftain should find his way down there at any point during the battle, simply let him charge, lunge, then side-step, turn, and assassinate. Easy.
The second the barrier falls, collect any needed ammo from the nearby Carbine crate and book it for the lower level of the bridge once again. You'll be safe there, and at the same time, you'll encourage your troops to move forward into battle. Chaos will ensue as grenade spam from both sides will nearly level the bridge, but it won't take long for everyone to die and the Pelican to swoop in to save the say. Once it does, exit the bridge via the original entry side, scan the area for any stragglers, and deal with them as necessary. Lastly, board the Pelican and call it a day. Fortunately for you, you will NEVER have to deal with that many snipers in this game ever again!