This is a guide on how to obtain all Halo MCC multiplayer achievements, be them Matchmade, Custom, Firefight or Forge. The explanation will be the easiest way to obtain them so even if an achievement can be unlocked in matchmade games I may list an easier method to achieve it in a custom game.

I am not planning on adding Spartan Ops achievements here even though they technically count as Custom Multiplayer games.

If I have missed an achievement please let me know in the comments section as well as any over relevant information or feedback you have! :D

• Halo Reach
  
• Halo CE
  
• Halo 2 - Classic Multiplayer
  
• Halo 2 Anniversary - Matchmade
  
• Halo 2 Anniversary - Custom games
  
• Halo 2 Anniversary Blast Soda Cans
  
• Halo 3
  
• Halo 3 Multiplayer Skulls
  
• Halo 4
  
• Cross-game
  
• Multiplayer wins

This achievement is awarded for getting a Skullamanjaro medal in the Headhunter gamemode. A Skullamanjaro is obtained by scoring ten skulls at once. This initially sounds hard but if you play team headhunter, when you or someone gets this medal on your team, you will get the achievement.
Play a standard game of invasion in Halo Reach and as the defending team, successfully defend the two marked territories to unlock the achievement. Can only be obtained as the defending team and in a matchmade game.

This is awarded for encountering a special location callout in a Multiplayer map. Can be obtained on Boardwalk by making your way to the location called 'Make Out Point'.

Here is a video guide by Maka91Productions if you need a little extra help: https://www.youtube.com/watch?v=IkzAuEhaNF4
Load up a custom game of Firefight on the map Overlook and head into the main base and go to the back of the upper floor and listen to the radio. These radios do appear on other multiplayer maps but this is a guaranteed method.

Here is a video guide by Maka91Productions if you need a little extra help:
https://www.youtube.com/watch?v=39E_h0g3HBU
Headshot opponents when they are sprinting. Can be obtained easily in SWAT games due to headshots being instant kills. You can unlock this in Custom games as well as matchmade. You can easily tell when you have done one because a Headcase medal will display. Headcase medals look like a six pointed gold star with a purple skull on top with a white target in the centre.

This achievement is awarded by completing 10 assassinations on enemy players in Halo: Reach. Can be obtained from custom games and matchmade games. To assassinate a player, follow them from behind and hold down the melee button.
The easiest way to obtain this achievement is to load up custom Firefight on the map Courtyard on Gruntpocalypse and set the starting weapon to a gravity hammer. Load into the game and use the gravity hammer to smash the forklift into a grunt and obtain the achievement.

Here is a video guide by Maka91Productions if you need a little extra help:
https://www.youtube.com/watch?v=m7FLRR0qBk8
Load up a game of Forge in Halo Reach (under the Create tab on the menu) and choose the map Forge World. Once in save the map as any name and the achievement will unlock.
Completing a matchmade game of firefight in Halo Reach is the easiest and quickest way to unlock this achievement, although it can also be obtained in custom Firefight.

Note: None of the Halo CE multiplayer achievements require matchmade play and can be obtained in custom games.

This achievement can be a bit time consuming to get right and is most easily obtained on the map Death Island. You will need a friend or second player to obtain this achievement.

It is hard to explain the method in words so it would be best to refer to this video by Maka91Productions: https://www.youtube.com/watch?v=gXxdCq0UDwE
For this achievement you need to start a custom game of Capture the Flag on the map Blood Gulch with 3 other players. Either find some friends or people willing to assist.

Pretty self-explanatory. You can load up different maps in custom games and then end the game straight away.

Can be down with the achievement above. Load up custom games with different game types selected. Just change the game type in the custom game selection i.e. Capture the Flag, Slayer etc.

All these achievements can be unlocked in Custom Games and do not have to be achieved in Matchmade games.
Find the Hippo on the multiplayer map Headlong on the yellow walls. Here is a video by Halo Completionist: https://www.youtube.com/watch?v=-SBQ6MSRZCg
These two achievements are easter eggs on the same multiplayer map, Coagulation. Here is a video guide by Halo Completionist: https://www.youtube.com/watch?v=StjEUoD4AJo
This easter egg is located on the map Beaver Creek at the top of one of the rocky walk ways behind a couple of loose boulders. Here is a video guide by Halo Completionist: https://www.youtube.com/watch?v=cUIP7BVFNEI
This hidden easter egg is located on the map Ivory Tower and can be unlocked by crouching in the corner at the back of the map by the elevator. Here is a video guide by Halo Completionist: https://www.youtube.com/watch?v=EAUbvLX7LkA
This achievement is unlocked by viewing one of the signs on the beach area of the map Zanzibar on one of the following days:

• January 1st - New Year's Day
  
• July 7th - Bungie Day
  
• October 31st - Halloween
  
• December 25th - Christmas

If you do not wish to wait for one of these dates you can change your PC's date and achieve it that way.
Pretty self-explanatory. You can load up different maps in custom games and then end the game straight away.
Can be down with the achievement above. Load up custom games with different game types selected. Just change the game type in the custom game selection i.e. Capture the Flag, Slayer etc.

For this achievement you need two double kill medals in a single game of Halo 2A multiplayer. Despite this achievement being obtainable in custom games, if you don't play custom games it will come a lot easier in matchmade games and you won't need to find people to do it with.

For this achievement you must kill someone with the 'Ninja Redux' achievement in a matchmade game. You will likely find and kill someone who has the 'Ninja Redux' achievement if you play a couple of games of Halo 2A multiplayer.

This achievement is awarded for getting a total of 5 Beat Down medals (meleeing an enemy player in the back) across any matchmade Halo 2A games. This isn't too hard nor is it too time consuming.

This achievement is earned for killing a player in Halo 2A multiplayer that has the Legendary Anniversary achievement (which is unlocked for beating the Halo 2 Campaign on Legendary difficulty). Although this achievement is obtainable in custom games it is easily obtainable in matchmade games, even more so than a custom game.

This is unlocked for ending someones killing spree (earning a Killjoy medal) in a matchmade game of Halo 2A. Will unlock with natural play of Halo 2 multiplayer. Note that this can actually be obtained in Classic multiplayer as well.

This achievement is earned for winning 10 matchmade multiplayer games while playing as an Elite. To play as an Elite you need to select it as your preferred species in the customisation page.

Self explanatory really. Be the top of the leaderboard on the winning team in a matchmade game of Halo 2A.

To activate the centre shield on the map Zenith you must make your way to one of the few control boxes and hold 'E'. This will activate it for a short time. You must do this 3 times in one matchmade game so try camping near areas where you can activate the shield.
Here is a video by Halo Completionist: https://www.youtube.com/watch?v=XAFJj0kaV2U

This isn't very hard and will come with natural progression in Halo 2A multiplayer games. You can also farm this in custom games with friends if you want. Examples of medals include double kill, killing spree, headshot etc.

For this achievement you need to obtain 100 splatter medals in Halo 2A matchmade games. Splatter medals are earned for running over or hitting enemies with a moving vehicle you are driving/piloting. This one is grindy so good luck. :D

1v1 Method: This can be earned 1v1 by you and a friend queuing up in separate lobbies at the same time. Only the map Lockdown will work. The player who is earning the achievement will need to shoot the ice and have the other player jump into the falling ice which will trick the game into awarding a Splatter medal. The ice will respawn after a short amount of time.


For this achievement you need to obtain 100 Environmentalist medals in Halo 2A matchmade games. Environmentalist medals are earned from killing enemies with falling ice on the map Lockdown and also from exploding fusion coils that result in a kill. This one is grindy so good luck. :D

1v1 Method: This can be earned 1v1 by you and a friend queuing up in separate lobbies at the same time. Hope for the map Lockdown or other Forge maps that have fusion coils and hanging ice.

Note: Some of these achievements can be obtained and have progression gained towards in matchmade games as well.
Can be achieved on any map and in custom or matchmade games. While you are in your controlled hill kill an enemy opponent who is outside of the hill 5 times. Despite not mentioning this in the achievement description, this needs to be done in a single game of KOTH. Each correct kill will grant a Hill Defence medal.

For this achievement you will need 2 other people if trying to achieve it in a custom game and make sure one player is on the opposite team and one is on your team. You must score the ball once, kill the enemy player once and pass the ball to your teammate once for the achievement to unlock. Can also be obtained in matchmade games.

Unlocked by taking, planting, and scoring from the bomb spawn without dying or dropping the bomb. This can be unlocked in custom games as well as matchmade games.

On some multiplayer maps there are explosive canisters called Fusion Coils. Shoot one of these canisters next to a player to kill them and unlock this achievement. Lockdown and Stonetown are good maps for this.

Unlocked by killing an enemy player in a Halo 2: Anniversary multiplayer match with a Sniper Rifle or a Beam Rifle while that player is zoomed in. Can be obtained in custom or matchmade games.

Load up a custom game of Territories (3 plots) and control all 3 zones for 30 seconds and the achievement will unlock. You do not even need a second player for this.

You can do this in a custom game by your self. Just load up a game of Juggernaut and survive for 30 seconds.

For 'The Goose is Loose' achievement you need a total of 25 kills with the Gungoose in matchmade and/or custom games.

For the achievement 'Top Gungoose' you can get it in a custom game on the map Bloodline with a friend. This method here by Halo Completionist is very easy: https://www.youtube.com/watch?v=Is-9aM9F3CQ

This achievement is easily obtained on the map Bloodline. You can farm this in custom games with a friend or in matchmade games.

This achievement can also be obtained on Bloodline as both bases have man cannons. Alternatively this can be earned in many matchmade and custom matches as lots of maps have man cannons. SWAT may make this easier as a headshot is an instant kill.

This achievement can actually be obtained by loading into a custom game of Bloodline and then ending the game straight away 10 times by yourself.

Can be obtained in a custom game with a friend by loading up the map Lockdown and shooting the icicle while they are standing below it. There are 3 icicles available.

Load up a custom game on 'Warlord' with the game type set to Slayer and wait standing next to the centre area where the active camo power ups spawn. Can be obtained in a solo custom game. Here is a video by Halo Completionist: https://www.youtube.com/watch?v=rBeo6z0RY5c

Load up a custom game of Shrine on Capture the Flag game type and head to the opposite side of the map from where you spawn. Shoot the orange crystal at the top of the enemy base and then grab the flag before the water stops. This can be unlocked in a solo custom game. Here is a video by Halo Completionist: https://www.youtube.com/watch?v=pd-_uZFFPyU

This can be unlocked in a custom game with a friend. I recommend loading up the map Bloodline and hijacking a friend on a gungoose or ghost. Do this 5 times in one match for the achievement.

For this achievement load up a match of Bloodline with a friend and let them fly a Hornet to you. Make sure you have a Rocket Launcher and simply blow them up for the achievement.

Simply get 25 melee kills in matchmade and/or custom games.

You can simply load into 6 multiplayer maps and end the game to progress this achievement but if you are going for all achievements you will unlock this naturally.

These collectibles are found on the Halo 2 Anniversary multiplayer maps. It is best to refer to a video when trying to track them down. Here is a video guide by Maka91Productions: https://www.youtube.com/watch?v=vS2CYjoqOfo
This achievement was added later on so does not count towards the BLASTacular! achievement. It is found on the Remnant multiplayer map. Here is a video guide by Maka91Productions: https://www.youtube.com/watch?v=MAq4X8KGQSc

All these achievements can be unlocked in Custom Games and do not have to be achieved in Matchmade games.
This Hippo can be found on the map Foundry. This achievement is probably easier done on Forge although you can find it normally without editing on Forge. Here is a video by Halo Completionist: https://www.youtube.com/watch?v=VfZqghlUEZA
This achievement can be unlocked on the multiplayer map Standoff. You want to make sure you have access to a Sniper Rifle so you could change the custom game options or game type to Snipers. Here is a video guide by Halo Completionist: https://www.youtube.com/watch?v=40UT7Xfo_xw
This easter egg is located on the multiplayer map High Ground. Here is a video guide by Halo Completionist: https://www.youtube.com/watch?v=9npwQNZrEf4
This achievement is unlocked by viewing two of the messages (located on the metal wall on the far side between the two towers) on multiplayer map Valhalla on two of the following days:

• January 1st - New Year's Day
  
• April 22nd - Earth Day
  
• May 5th - Cinco De Mayo
  
• July 4th - Marathon reference
  
• July 7th - Bungie Day
  
• October 31st - Halloween
  
• November 11th - Veteran's Day
  
• December 25th - Christmas

If you do not wish to wait for one of these dates you can change your PC's date and achieve it that way.
Pretty self-explanatory. You can load up different maps in custom games and then end the game straight away.
Can be down with the achievement above. Load up custom games with different game types selected. Just change the game type in the custom game selection i.e. Capture the Flag, Slayer etc.

These collectibles are found on some Halo 3 multiplayer maps (the Mythic Maps). It is best to refer to a video when trying to track them down. Here is a video guide by Maka91Productions: https://www.youtube.com/watch?v=jN5LHceUd3E

Pretty self-explanatory. You can load up different maps in custom games and then end the game straight away.
Can be down with the achievement above. Load up custom games with different game types selected. Just change the game type in the custom game selection i.e. Capture the Flag, Slayer etc.

Note: Some of these achievements can be obtained and have progression gained towards in matchmade games as well.
This achievement is for 2,500 headshots in multiplayer. Progress can be gained from both matchmade and custom games and will likely unlock by natural multiplayer play.

This achievement is for 2,500 assist medals in multiplayer. Progress can be gained from both matchmade and custom games and will likely unlock by natural multiplayer play. Spartan Ops also grants progress towards this achievement. Note that Halo 3 does not grant assist medals.
Halo 3 does now count after a recent update.

Beat Down medals are awarded for killing an enemy with a melee from behind (that does not result in an assassination). These can be earned in matchmade and custom games and even Firefight games.
For this achievement go to the custom games multiplayer page for Halo CE and save a custom game variant with the name '.fortune' and the achievement will unlock.

Although the achievement is unlocked from the Halo CE page it counts as cross-game within the MCC.

This is awarded by being killed in a manner which is unrecognizable to the game engine. For example, getting killed by environmental objects (such as the train on the Halo 2 multiplayer map Terminal).
Like the above achievement, save 5 custom game files for this achievement. Can be obtained in any Halo game.
Save 5 maps in the Forge gamemode accessible from the main menu under the 'Create' menu.

Double Kill medals are earned for killing 2 opponents within 4 seconds of each other. This medal is represented by a gold circle with 2 blue stars. This will most likely unlock naturally by playing most matchmade gamemodes and is not that hard to obtain.
Double Kill medals earned in matchmade Firefight do count towards the achievement.
Killing Spree medals are earned for killing 5 opponents in one life (without dying). Dying resets the counter. This medal is represented by a steel 4-sided star with a cyan target in the middle. This will most likely unlock naturally by playing most matchmade gamemodes and is not that hard to obtain. Can be easier on objective gamemodes if you are struggling cause opponents attention will most likely be on objectives rather than you.
Killing Spree medals earned in matchmade Firefight do NOT count towards the achievement.
Killjoy medals are earned for ending another persons killing spree. This medal is represented by a smiling face with a red line through it. Just play lots of multiplayer games or alternatively if you wanted you could find someone to farm it with in 1v1 gamemodes.
It's worth noting that sticking someone with a plasma grenade does not count towards the achievement. Also avoid Halo 3 and Halo Reach when aiming for this achievement because they do not have grenade kill medals.
There are six legendary medals in Halo MCC which are:

• Steaktacular - achieved by winning a slayer match with at least 20 kills more than the opposing team.
  
• Extermination - achieved by killing the last alive player on the opposing team with at least an Overkill that results in the entire team being dead at once.
  
• Killionaire - awarded for killing ten opponents within four seconds of each other.
  
• Perfection - awarded for winning a Slayer game with at least 15 kills, and without dying.
  
• Triple Double - earned by finishing a game with double-digit kills, assists, and headshots.
  
• Unfriggenbelievable - awarded for killing 40 enemies in a row without dying.

Firefight variants do NOT count for the achievement.
Unlocked by earning a total of 250 Capture the Flag mode-specific medals. CTF mode specific medals are easiest obtained in Halo 2A and Halo 4 multiplayer. Medals included can be found under the career tab.
Unlocked by earning a total of 250 King of the Hill mode-specific medals. Again, Halo 2A and Halo 4 contain the most KOTH medals.
Very easy and will unlock probably after a single matchmade game.

These achievements are earned for winning both matchmade and custom games in any gamemodes across any games.