From Halopedia, the Halo wiki
This is a walkthrough for level Data Hive. It is written for play on Legendary, with notes for lower difficulties.
This is your first mission as the Rookie that isn't part of Mombasa Streets. If you've made it this far hopefully you've still got your SMG and Pistol (they're also your defaults if you're playing out of the Menu) as they're going to be the most helpful in this level. Good Skulls for this level are Catch, Cowbell and Grunt Birthday Party.
You know, this would be easier if I could just slide right down to 9?
You start this level in a room that has grenades and two Shotguns. If you're comfortable with the Shotgun you can swap it out for your SMG but keep your Pistol for its headshot capability. Proceed through the doors and follow the winding path down, you'll run into Grunts and Jackals, but they're easily handled with the pistol and a few melees. Once you've passed the long hall you enter the first set of rooms, they all look the same and there are some twists so use your VISR map to get a good look of what's ahead of you. Proceed cautiously through the rooms, killing the Jackals and Grunts with your pistol, while luring the Brutes into the confining hallways and sticking them with Grenades. If you aren't judicious with your Magnum ammo, pick up one of the many Carbines as there's lots of ammo for them and with a steady hand it's just as accurate as a pistol (and it comes in handy killing Brutes). When you get to the end and meet the NMPD officer, drop the Carbine and run back to find a Spiker or Needler before you raise the Data Stack. When you do open it, take cover and let the drones fly up, the NMPD officer will help, but you're better off using him as a distraction and killing the drones with the Spiker.
Damn Dirty Apes...
Before you drop down, pick up your carbine again. Once you've dropped, creep through the doors and kill the two Drones quickly. The NMPD officer goes straight for the tunnel on the right, and you can follow him, but you're better off picking off the two Grunts at the other end. The Brute down there will point and growl but won't move up. Once you've gotten rid of the Grunts, follow the NMPD officer through the side tunnel. When you come out the other end, stick the Brute with a plasma or spike grenade. Continue forward slowly, letting the NMPD officer distract the throngs of Brutes, letting you pick them off with assassinations and grenades. Occasionally you will have to stand up and fight the Brutes. If you run out of Carbine ammo, pick up something else, Spikers and Needlers and Maulers are around as well as Shotguns, so use them instead. Kill them quickly and move on to the second set of rooms. In here is more of the same, take out the Jackals and Grunts and lure the Brutes and grenade them to death. It's made easier (or annoying) by your NMPD friend who distracts them, although he can't seem to kill anything. Once you reach the second drop, take a minute, run back, pick up any grenades you can from the rooms if you're short and make sure you have your main weapon (preferably the Carbine, as there's ammo around) loaded up with as much ammo as you can find. If you don't have all 30 Audio Logs then the officer will follow you, if not, bid farewell as he will be killed by Drones.
One of These Things is not like the Others....
Once you drop down to Sub-Level 09 you'll notice it's frozen over. Let your buddy distract the Brutes, there are between six to eight depending on difficulty and on legendary they're harder to kill so take your time and clear them out. There's a Chieftain here, with his infinite and portable Plasma Cannon. Kill him quickly with an incendiary grenade or headshot from the carbine, or plink away his shields at range until he charges and then hit him with a firebomb. Either way with this Chieftain your best bet is an incendiary grenade, because of the close quarters and the plasma battery. Once you've cleared out these Brutes, the officer is going to open an extra door (if you have all the audio logs) and you're going to have to kill him. Take the Plasma Cannon, it's quick and it doesn't waste any ammo you're going to need later.
If you had to kill the NMPD Officer, leave the little room and go to the end of the alcove to your left. You can pick between two choices: a Flamethrower, or the Plasma Cannon that you took from the Chieftain. The Flamethrower is the best weapon for the next part (and also needed if you want the I Like Fire Achievement). Be careful though, the Flamethrower can hurt you as much as it can hurt the enemy and a little goes a long way. Go down through the door and follow the hallway, you'll run into a mess of Grunts, Jackals, Drones, and a few Brutes. Quick controlled bursts from the Flamethrower and it doesn't matter what difficulty you're on, the only way you can screw it up is if you flame broil yourself. You should have around 80 ammo or more left in the flamethrower if you just kept tapping the trigger in the little fight before you run into Dare.
Man, I need a can of RAID! (or, Why did they stop making DDT)
Once you're done with the cutscene, use your flamethrower in the next section to quickly clear out the enemies. Make sure you heal up as you move along. The drop and occasional spatter of flamethrower will drain you quick and you need to be at full health for your run through the hive. There's only a few enemies along the way, but they can drain ammo dodging in the large room, so use the rest of your flamethrower and drop it. After you come out into the first hive section, before the elevator, look to the right and drop whatever you're carrying for the Beam Rifle, your other weapon should be a Carbine, and here's where it comes in handy. Follow Dare over to the elevator and bring up your Carbine. Follow Dare around the hive. The pesky Drones are everywhere, keep moving! Short bursts from the Carbine will drop Drones quickly and accurately. There's a lot of them, but a combination of running and shooting keeps you alive. You can also drop down the middle of one of the center rings to give you some cover to recover your Stamina. If you get to the end of the hive and see the door, just go through. Dare will magically appear. She will have gone to the left of the tunnel. You should go right. Drop down, and bring up the beam rifle. Zoom in and you should get a good look at the Chieftain and one of the minor Brutes. Don't go down yet. Use two shots on the Chieftain and get him to bring up his invincibility. While he's untouchable, Snipe out the other Brute you can see, if you can get both, so much the better. When the Chieftain's invincibility drops, Snipe him to death. Drop in and swap out both your weapons for a full Brute shot and the Gravity Hammer. If you want a silent option, jump down and run to the Chieftain and his buddies and hide behind a stack of boxes so the Chieftain won't see you. When he isn't looking, run behind him and quickly assassinate him. It may take a couple of tries, but in the end you'll get him. For some strange reason, the two other Brutes won't notice this and will keep attacking the door, so simply assassinate them as well. If you still have your Flamethrower then it will really come in handy once you come out of the Superintendent's Data Center.
The Best Defense is to Hit everything as Hard as you can.
After the cutscene, your job is to kill everything that moves and keep Vergil alive. Buck and Dare help a little, but not much. Come out swinging, Gravity Hammer and grenades. Kill the Jump Pack Brutes the minute they touch down and throw lots of grenades, swap in your Brute shot and kill the Grunts and Jackals. If you still have your flamethrower, then just spam the trigger. Don't hold it down, just tap it repeatedly at any enemy you see. Vergil's overshields should keep you alive on your road to pyromania. If you don't, wade in further with the Gravity Hammer and grenades and finish off the stragglers. After you clear out that room before you move on, dump your flamethrower as you won't be able to carry it on to the next level, and it will be pretty much useless. Be swift and silent through the next area heading quickly through the door on the left to avoid a fight with the Drones. Once Vergil opens the door, stealthily pass through the next drone filled hallway without a fight. Once you and Vergil are on the elevator the level is completed. Keep your full Brute shot and Beam Rifle to get you started in Coastal Highway.
Notes for Lower Difficulties