Story related achievement for completing the 10th and final level, The Maw. Skulls do not affect achievements so feel free to make this as easy or hard on yourself as you want.
During this level you can earn the following achievements. I will call attention to them later as well.
Level walkthrough:Part 1: And the Horse You Rode In On
In the final level you will be pitted against Sentinels Flood and some occasional Covenant. Stick to weapons like Pistols or Shotguns. Frag grenades work great on Flood.
The layout will look familiar to the first level because you are back on the Pillar of Autumn. You may remember the mess hall from that level. Take out any infection forms and wait for a Hunter to show up. Let him take out some flood, but try and pop a pistol round in his back when you get a chance. The partner to the first Hunter will burst through a door and head in to the mess hall for the flood if you don't kill him first. Take him out the same way.
Keep moving through the level picking off enemies or running past them as you please. Take note of SpecOps grunts as they love to throw grenades. Don't forget the needler can make quick work of Elites you encounter, but I recommend keeping you your shotgun and pistol combo after the dust settles.
On harder difficulties the noob combo of plasma pistol/pistol works wonders. An Overloaded plasma shot + a few shots can take down any elite. You eventually com to the bridge and you'll trigger a cut scene.
After the cut scene ends use the cover to take out the Sentinels and keep moving. You'll move through lots of flood, a pair of hunters and an elite. After them you might want to grab a covenant weapons because there are sentinels coming. Kill Sentinels then flood.
You'll be near the cryo chamber where you start the game and there's likely already some fighting going on. You can go up the ladder and skip this whole battle.The Terminal for this level is located in the upstairs of CRYO B on a red screen.
Assuming you picked up all terminals up to this point you should also unlock the following achievement:
There's a really hard battle just past the control room. I almost thought this was an infinite spawn of flood on Legendary, but it does end I promise. Try taking our carrier forms to maximize damage, but watch out for flying grenades and rockets. Pick up a health pack before leaving. Make sure you grab a rocket launcher and as much ammo as you can get. There's also an overshield in a dead end hallway.
You'll enter some tunnels where there are lots of exits. Far left leads to a room with dead elites and plasma grenades. Far right is blocked, but there's a health pack with some frag grenades. There are sentinels and Covenant duking it out. Once all the sentinels are dead flood will arrive. If you want to use your rockets here to clear out the straggles that is fine, but keep your rocket launcher. Follow the red arrows towards the armory.
Grab all the shotgun and rocket launcher ammo you can hold. There's a surprise of Flood with Active Camo at the back of the room so watch out. Part 02: Light Fuse, Run Away
Cortana will tell you what you need to do. You have to open the valves to the reactor and then either fire a rocket or throw a grenade while the reactor is open. I highly recommend using the rockets. There are checkpoints, but they are spread out so try to not die.
You can always go back to the armory to restock. There are eight health packs on the on the first floor.
You have to make it all the way to the third level where you hit the switches. Order does not matter. After you hit a switch, jump onto the pipe and ride it back across the room. Fire a rocket at the bright spot, making sure the slits are open. You'll have to blow up each one before beginning the final phase of this level. Follow the waypoints. There's not many enemies but still be alert. There are some covenant on the elevator with fuel rods so watch out. If you've got any rockets left over you can just fire one there and be done with them. You won't need ammo soon anyway and the countdown timer has not started so you're not in any danger despite Cortana's pleading.Part 03: Warning: Hitchhikers May Be Escaping Convicts Note: Starting here, if you are going for either of the following two achievements, make sure you revert to the last checkpoint if you screw up too much.
If at ANY time you are ejected and have to get back in, you need to revert to the last checkpoint. Also, if you are trying this on Legendary you may just want to do it on Easy to earn this achievement.
This can be a challenge so I suggest being familiar with the layout. Preventing flips and getting stuck is the best way to maximize time. I would also highly recommend not trying to get the skull at the same time. Getting out to get the skull is a huge waste of time. If you need to get the skull it might be best to just play this again on easy.
The countdown starts as soon as you enter this room so grab the first warthog on the right. If at any point you flip your Warthog just get back on and keep going.
Stay in the middle as you enter the first room. Drop down, but as you go back up steer to one side. Go around the blockage then continue down the middle for the rest of this room.
Travel through the first hallway just making sure to stay on one side as you enter the next room.
I suggest using the sides of this room as I always have bad luck flipping down the middle path. Whatever works best for you. If at any point your shields are down it's not a bad idea to try waiting to let them recharge. Better than dying.
There's a shortcut in the next hallway if you go to the left of the first column, then to the right of the second column, then swing around and take the hall to your left. If you can't do this just skip it. It's not that big of a deal.
The third room has a wall blocking the entrance so enter at an angle and stay near the walls. Stay on the catwalk and you'll breeze through here. Keep moving through the next hallway and into the 4th room.
You have to zig zag around these pillars then stick to the middle path.
The next hallway leads to the bridge where you are supposed to meet Foehammer. If you still need this skull you'll have to stop and get off your warthog to get the skull.
If you already have the skull just keep on moving. Stopping here is just a waste of time *sniff*
Assuming you picked up all skulls up to this point you should also unlock the following achievement:
The next hallway has a short cut on the right. After the second column.
Cortana will now warn you of a large jump (there's actually two). This is a challenging spot for many and may take a few tries to get right.
Get as straight as possible and just put the peddle to the metal. Floor it then ease up on the pedal when you're in the air. This will stop you from flipping over and wasting time.
You should see the hangar opening up. At this point you have to get out and run the final part. There are still plenty of enemies between you and the longsword. to avoid them just get out of the middle (I usually go left)
If you want some fun it is possible to grenade launch/rocket launch your warthog over the obstacles. Then you can get back in and ride the rest of the way to the longsword.
None! You're Done with Halo CEA. If you want to go play Halo 2 PC feel free!
Edit: For anyone who gives a negative on this can you explain why? There isn't much to the level related achievements so not sure what more you want this to say, but I'll add it if you feel it's relevant.