Floodgate - Cleansing
It Followed Me Home
Ah yes, your favorite enemy in Halo, the Flood. Finally, at last! No but really, those Flood levels from Halo 2 still haunt me.
Now you must backtrack a bit. Just keep moving to the tune of men screaming. You will eventually arrive at a spot where some marines are camped out, but of course you know that won't last. The Flood are back with a vengence! They drop down by the door and you had better toss a bunch of grenades their way. Kill what ever survives but watch out for those marines of yours, they will most likely turn, so take them out once they do. If I'm not mistaken, the Flood will reanimate dead Flood victims, so you can't rest until all the little critters are all dead.
Once things are relatively safe, go behind the sandbags for some guns. Now might be the best time to carry a Shotgun, if you have never used one up to this point. Take the path around the door to encounter more scourge, and don't think you can save any of the marines, you can't. Move into the room where you first fought the Hunters to find a lot of Flood-things in the area. There are marines in here, but good luck saving them. Just get in close and use your Shotgun to its best.
When all is clear, collect the ammo and grenades and move along. Follow in your footsteps (a common theme in Halo) and fight the Flood in the storage area. Always use the Shotgun up close, and get the ones that jump while they glide through the air. Keep moving and go up the steps on the right. Don't miss the Flamethrower on at the top. Pick it up and follow the Arbiter. Drop through the hole for another moment, and then keep up with your friend.
At the sandbags is a decision time moment. Yes, there will be many Flood in the weaving path up ahead, but your Flamethrower is not the best weapon for the occasion. You can drop it and fight the Flood as before, or you can try your best shot with the fire gun. Either way, enter the winding area and take out the Flood. When using the Flamethrower, resist the urge to aim low and always keep backing up (and by urge I mean the auto-aim feature, you will have to fight that). The gun actually works well, just keep aiming a bit up at all times.
Where there was once a bunch of wounded and steadfast marines, there is now just one man in need of a happy place. There is a piece of equipment behind the sandbags called a Regenerator, so get if if you please. This thing will keep you healthy in the heat of battle, I think. Keep moving back out to the field where you matched wits with the Scarab.
Shadow of Intent
At least you get some good news: the Elites have decided to show up. Move along the walkway and take the ramp down to the fight, which you don't even need to help the dudes with. Move with them and it might be best if you drop that Flamethrower now.
The group will run into an ambush of Flood, so be surgical with your Shotgun. Lots of Flood will jump from the left of the cliff and seriously mess you up, but just don't die, and try not to kill your friends. Near the ramp there will be a pregnant Flood-thing, so grenades are in order here. You may lose some Elites, but that just means a free Energy Sword for you. Swap it with your rifle to have all close-quarters weapons on hand. Move up the ramp and move inside the place where you suited up for that Mongoose battle.
*NOTE: You may want to hold onto your Battle Rifle, if close combat isn't your strongest skill.*
*NOTE: My Arbiter got stuck here, so if your's does too, just nudge him in the right direction.*
Down the corridor is more Flood, but a lot with guns. Either toss grenades like crazy, or get in close. At the closed door will be another ambush from above. Then more will come in from the walkway above the door. You can run up the ramp on the right to get in close. After the encounter, consider picking up that Battle Rifle on the floor.
Follow the walkway to the next room and then go outside. You learn of Cortana's survival, and then you run into a Flood-Hunter. The good news is that these things are slow, just pull out your sword and slash them. Then more Flood will greet you. Go to the left, jump on the turret, but quickly detach it so you can avoid all the attacks and leaps from the Flood below. Kill anything that moves in the shadow and then move along either the lower path, or raised path.
More Flood to jump in, so keep dispatching them, and I recommend you take the higher path if you have the turret. Not far you will run into some new kind of Flood that are moving turrets. Use your Battle Rifle on these things, or get up close. You can tell which ones they are because they will look like moving legs when not shooting. After you run into a near what I presume is the crash site, get out your Energy Sword and just start hacking through the almost countless Flood-things. There will be marine, Brute, Hunter, and turret Flood all in one small area, and make sure to go for the Hunters first.
Then you will overlook a strange area of debris below. Hop down and you can stock up on supplies, but you don't really need to. Move up the wreckage and drop down.
Infinite Devil Machine
Move along for a new type of moment, a Gravemind moment. There will be plenty of swords along the way, so you might switch those for your Hammer, if you must. Drop down another hole and proceed through the creepiness. Another moment and then jump onto the blue glowing thing on the floor. Retrieve Cortana for a scene. And then the plot thickens... end level.
*NOTE: Did anyone else notice how a computer is affected by... physics?*