Tom Clancy's The Division 2

To unlock this achievement you need to beat the Operation Dark Hours Raid in a team of 8 players. It's also worth noting that you can land on the final boss via matchmaking and avoid having to fight the previous 3 bosses and if the team is successful and there are 8 of you when it is beaten, the achievement will still unlock. Though where you are put in the Raid is random as is the nature of matchmaking.

First, while it is not required when matchmaking and is not something I did, communicating via headset would make this significantly easier, at least on the final boss as it is very involved and having everyone do the right thing at the right time is difficult to communicate to everyone without speaking. However it's certainly possible to do this without if all 8, or at least most of the 8 players are all somewhat versed in what to do.

You will need to be in World Tier 5 and have a Gearscore of 490 or above to even begin this Raid so if you're below that then you will need to keep grinding out the main game's missions to unlock higher World Tiers and to find better equipment to raise your Gearscore. Also it's not much use to just throw together what you have for the sake of getting a high enough Gearscore. You should try to make a competent character with weapons and equipment that are useful to yourself and your team. High armour, armour regen and healing abilities are recommended as a priority, though Damage to Elites is a huge advantage since most of the enemies will be armoured to some degree. Once you have the required Gearscore and a competent character build, you're ready to take on the Raid.

The Raid is set in stages and each has a boss to be defeated. These aren't the same as the bosses from the main game that are simply high health and can be brought down by overwhelming firepower. Instead, they typically have a mechanic that needs to be exploited so that you can damage and defeat them. At this point, if you matchmake you are likely to land on a team of people who all know what to do, I consistently got to the final boss with the random teams I was put on as it seemed most of the time, most of the players knew what to do.

A basic breakdown of each boss and what you need to do to defeat them is as follows:
 

• Boomer:
  • Boomer is the first boss and when he appears you will need to damage his backpack to bring him down to his knees. Once here you can do damage to his armour/health bar. When he stands back up you need to keep damaging the device on his chest to stop him from healing himself. Repeat this process to defeat him. Also try to keep him away from the terminals that are emitting a blue light as this will give him immunity from damage. You can get his attention by attacking him and there will be a red eye symbol over the player that has his attention.

• Ricochet, Dizzy and Weasel:
  • At first there will only be Ricochet and Dizzy to deal with and each will spawn in a different side of the room that is split in half. There will be a series of buttons in the middle of the room that presents a puzzle that needs to be solved to stop poisonous gas from entering the room and damaging the players' health bars. After either of these two is defeated, another boss, Weasel, will spawn. He's the same as Ricochet and Dizzy and is just a heavily armoured enemy that takes a lot of bullets to bring down.

• Buddy and Lucy:
  • Buddy and Lucy are two robotic dogs that have an attack that can down you instantly so remain in cover for the duration of this fight and only appear to deal damage when you know it is safe. The general strategy for beating these is to damage them as equally as possible and to keep them separated since Buddy has the ability to heal them both, dragging the fight out longer than it needs to be. You will also want to try and kill Buddy first as killing Lucy first can trigger Buddy into using its heal and prevent you from damaging it.

• Razorback:
  • Razorback is the final boss and will take some co-ordination to defeat. It cannot be defeated simply by shooting it. You will need to follow a process to expose a weakspot so that you can deal damage to it. The fight is also in multiple stages. During the first stage you need to stand in the circle around the four generators that are at each corner of Razorback. Doing so you will see a counter raise to 100%. Once all four of these are at 100% you will see at the front and back of Razorback that there is now a red light behind a grid. Shoot these grids, both can be destroyed from a single Crossbow bolt if this is your specialty, then throw a grenade inside and after it explodes the red light will turn green. Do this to both grids that have a red light on them to turn them both green and then the top of Razorback will open and a huge panel will rise out of it. Go around to the back of it and you will see two batteries, of sorts. Shoot these to destroy them. Once these are destroyed a weakspot will appear towards the top of the panel. Shooting this will deal damage to the boss. You will have only a short time to perform each of these actions and taking too long with any will reset the boss and you will need to get all four generators to 100% again. The most damage you can do to Razorback in a single successful attempt at exposing its weakspot is around a quarter of its total health, so you will need to repeat this process at least four times, though it will likely take more than four.
    
    While all of this is happening you need to be aware that your entire team can be killed via a wipe mechanic. When you hear an alarm look to each of the four corners of the arena and you will see one of the Rocket Launchers there with a glowing orange light. Make your way here and destroy the enemy with a minigun as quickly as you can. If you leave them, they will activate the Rocket Launcher and your entire team will be killed, reseting the entire boss fight.
    
    After you have brought Razorback's health down, there is one more objective to complete. You will see each of the four Rocket Launchers at each corner of the map has a number on it, from 1 to 4. You need to destroy these in order. If you go to the back of it there will be a computer console that can be destroyed but you need to wait for it to be activated before you can destroy it. You simply shoot them to destroy them. It is worth trying to have your group split in 2 groups of 4. Have group 1 at Rocket Launcher 1 ready to destroy it and group 2 at Rocket Launcher 2 ready to destroy that. When group 1 has dealt with Rocket Launcher 1 and group 2 are waiting to destroy Rocket Launcher 2, have group 1 run to Rocket Launcher 3 and get ready to destroy it, then when group 2 are done with Rocket Launcher 2, have them run to Rocket Launcher 4 ready to destroy it. If you fail to complete this section, your team will all be killed and the boss fight will reset and need to be completed again, from the beginning.

Good luck. The achievement and some decent loot will be yours upon Razorback's defeat.