Halo 5: Guardians

This one is actually pretty simple.
Just rush through the driving section, skipping as much combat as possible. When you do have to use your weapons try and use automatic weapons to remove extra armor off enemies. Then use an accurate weapon (pistol, BR, DMR) to finish off damaged enemies. When you get to the Promethean Knights try to shoot for the glowing bits on each side of their head. Once one is shot off they will yell, exposing their face for a easy headshot.

In addition, if you go down and are revived you can still get this achievement. If you die and you are quick enough you can pause and reload your last checkpoint (at least I was able to).

All in all, you just want to run through as quickly as possible avoid combat where unnecessary. I hope this helps.

EDIT: As Psyburns notes in the comments, when playing through on co-op it would seem to be a good idea to enable the IRON skull. That way if anyone died it would automatically reset you at the last checkpoint.
Thanks Psyburns for the tip.

Here is the easiest way I did it. In the video it shows taking the warthog all the way to the elevator. However, if you command a squad member to get in the warthog before you hit the elevator command it will stay for the duration of the mission. Super easy.

Here's a visual guide where I can confirm the great pointers in the other solutions. Reloading checkpoints even if you die works. Heroic really isn't nearly as bad as Legendary. Skip through everything except the battle at the elevator and the gate before. Good luck.

For those of you that started on Legendary and thinking to yourself "How in the hell is this going to be possible in 18 minutes without dying?" The difference between heroic and legendary is bigger then its ever been in any halo campaign. This may be in part to the fact you can now be revived and being 1 difficulty level lower means that you AI allies can take more hits before going down themselves which means you have a better chance of being revived and your AI buddies can also dish out more damage before becoming a nuisance on the ground. P.S. I did do this solo and was downed once but revived, the achievement is still valid as long as you don't fully die.

This achievement is actually quite simple and I'm sorry I forgot to record my successful attempt (which was the first try when I was just trying to gauge how hard it would be), so a text one will have to do. :)

Firstly, begin the level by sprinting close to the left side of the fence, if you are sprinting and you jump and 'jet pack boost' (LB on Recon controls) right as you leave the ground you get a large speed boost, continue to do this until you get to the warthog on the left. Get in and do not wait for your allies, drive fast and ignore everything until you get to the tunnel. When you get there an enemy warthog and gunner will be driving down the tunnel, wait just inside the entrance of the tunnel and let them drive until they are about 1/2 way down then haul-ass down the tunnel past them and continue on to Meridian station. (I saved my checkpoint when I got out of my vehicle but I regret to say I'm not sure if reloading your checkpoint is acceptable for this achievement as I only needed 1 try to complete it.) Push the right side of the base first clearing out the soldiers and crawlers in a timely manor, up to the large monster truck that you can walk under, take out the gunner in the gauss turret on the left side building at the top. Then the two soldiers on the walkway to the right, next to the building at ground level. After this proceed to eliminate the snipers that are at the top of the building on the right (POV reference: facing the door that you need to get open). *NOTE* The snipers dropped down for me to the ground floor, they are weak and can be killed with a few headshots but they might not do that for you as with all AI based games. After you clear the snipers push all the way up to the last wall before the door but don't go past, there will be a large group of crawlers that will spawn and move past the wall and come into your side of it, kill them and clear out the rest of the enemies on your side of the wall. Next there should be BR if you need it in the building that the two soldiers were on the walkway beside (i.e. the building with he data pad in unconfirmed), grab that if you need it as you'll need a longer range weapon. Order your team to start to clear out the section by either targeting individual targets or by ordering them to go to the door (this will probably kill them but they will at least do some of the work and leave you to shooting as opposed to ordering them to kill each individual target), taking out the gunner on the top of the ramps left side is the priority here.

After this you should get to the elevator ASAP by just standing near the door to it until it opens after the talk you have with Governor Sloane. Clear out the enemies here ASAP (I recommend sending your team down the left or right side and you take the other side). After you clear out the enemies get to the control panel ASAP and hold down the action button as it will work before there's a prompt for it. Next go to the small buildings that you can go into by smashing the upright vents (below the outer catwalk). In one of the there should be a railgun, take this. Stay on the outer catwalk for this whole section (drop down if you're very low shields) Try to get to where the enemies spawn (blue flashing electricity domes) and throw grenades prior to their actual spawn, trying to time them to explode right as they appear, if this is done correctly there will be no crawlers left and only a few soldiers. There's two waves of meh, enemies. Clear them out with haste as the faster you do this the faster the elevator starts to move and it won't move until every last enemy is dead, the railgun is a 1-shot-1-kill on any captain or solider, use it. The last wave will be three knights (your team is useless in killing knights) so you'll have to kill them yourself. Shooting the head takes time but you can do it if you have the ammo. I'd suggest placing your team on the other side of the knight from you so it's back is towards you and it's shooting at them, and shoot the glowing circles (they look like vents) on the back of its armor to destroy 1/2 of it and reveal a glowing circle on its back, two shots to this should kill 1 knight.

After this section you basically just run the rest of the level without stopping for anything or anyone. Run up to where the Promethean ships appear and keep going (this is a starting reference point) up the stairs and to the right going all the way around the pillar and jumping up onto the next level, up the stairs there jumping across to the right again going all the way around, up the stairs twice, jump onto the ramp that falls down from above, keep going on the linear path from here until you come to a large set of stairs with a Promethean running away from you and there's two light rifles resting on a ledge, sit on the catwalk and kill all the watchers (3 I think) shooter 2-3 soldiers until they're dead (on the first level of stairs closest to you) or a captain if you're feeling good. Once there are only a few left book it the fuck out of there. Straight through the catwalk up two sets of stairs, right then left up stairs past the soldiers at the top make a quick right and start jump boosting, go left towards the platform and sprint it the fuck to home, you can make it to the platform he pelican is on before the first shock wave hits, and when the first shock wave does hit the level automatically ends if you're near that platform. DING ACHIEVEMENT. Thanks for reading all of this, once again apologize for no video I thought this would be harder then it was.

So your main strategy is to rush two parts and spend the majority of your time in the middle of the level. At the start is a brief driving section, you want to power through this as fast as possible and basically ignore everything.

Then, you will get to your first fighting area. Take some time here and take advantage of the snipers placed up high. NOTE: you can go down and have your team-mates revive you. That doesn't count against you. If you die, quickly pause and load from last save.

The same strategy applies as your going up the space elevator. However, when you get to the top, you want to just sprint past as much as you can. If you do it right, and get a little lucky, you should only need to kill 2 or 3 people here. If you follow this, it should be done between 13-15 minutes, so you even have time to spare.

Video guide found here: