Halo Infinite

This achievement takes place in the first mission : Warship Gbraakon.
There's a total of 11 different weapons (one of them being a turret : the Plasma Cannon you can find midway through the mission) and 3 different grenades.
MAKE SURE TO GET DIRECT KILLS WITH EACH WEAPON AND GRENADE.
No splash damage, chain reactions or whatnot. for example, if you shoot the hydra or throw a grenade near a fusion coil, make sure the kill is credited to the weapon or grenade and not the explosion of the fusion coil.

At the moment, this achievement seems buggy and not unlocking for many while meeting all the requirements : A recurring theme (that apparently still doesn't guarantee the achievement) is that you'd have better chance on a fresh save instead of using Mission Replay.

Here's the full list (in order of appearance) and where you can find them :

• MK50 Sidekick & MA40 AR : You begin the mission with these two weapons.
• CQS48 Bulldog & BR75 : The Bulldog shotgun will be just above you at spawn. The BR will be on the left side of the room. It's position will vary : it spawns in a garbage dump along the left wall of the room, a claw machine will then grab the dump to drop it next to the Red Energy Shield.
• Plasma Pistol, Needler & Mangler : You can find them on Weapon Racks throughout the mission (as early as the hangar you spawn in at very begin the mission).
• Pulse Carbine : Can be found on the ground here and there, but you'll first find it in the huge room just before the elevator. Pretty hard to miss, it'll be lying on a crate just to your right when you first enter this room.
• Frag Grenades : Hard to miss, the first frag grenades you'll find are just on your way right after the Elevator.
• CQS48 Bulldog : If you missed the Bulldog in the hangar, here's your last chance : straight after the Elevator, go to the room where the first pack of enemies you see spawned, it'll be on the ground to your right.
• Spike Grenades : Not long after the Elevator, you'll go through a room with a bunch of brutes and grunts and an AR holograph in the middle of the room. On the weapon rack in the back, there will be your first spawn for the spike grenades.
• Plasma Grenades : In the next room, with a bunch of brutes and grunts, in the far back, you'll find a Weapon Rack with Plasma Grenades.
• Plasma Cannon : Not sure if this one is needed, but after the room where you can get Plasma Grenades for the first time, there's a small blockade with a Plasma Cannon.
• BR75 : Not long after the Plasma Cannon, you'll arrive in a room with 2 holograms of Atriox ; to your right, there should be a BR against a crate in case you missed the one in the hangar at the beginning.
• Ravager : When you arrive to the Control Room of the ship, one of the brutes has a Ravager. There's also a Weapon Rack with a couple Ravagers in the far back-left corner of the room, bottom floor.
• Hydra : At the end of the mission, after grossing the gap of falling structures, the hydra is hidden behind some crates on the left side. You still have a couple grunts just a bit farther if you killed the enemies in the immediate vicinity of the hydra.

If you'd like a more visual guide, Maka91 uploaded a video guide of this achievement :

EDITS :
Kornack50 pointed out that, in coop, if one person does it, everyone gets the achievement.
IVIr IVIeNsA pointed out that the BR also spawns in the Hangar at the very beginning. While looking for it I also found out the CQS Bulldog Shotgun also spawns in this room.
Dreadful Chaos pointed out you could do the achievement with weapon variants (ie : Hydra & Ravager variants) you'd have brought with you through Mission Replay.

To unlock this achievement the fireteam must collectively secure at least one killing blow using each of the 10 weapons, 3 grenades, and 1 turret commonly found in Warship Gbraakon. The achievement will pop for all members of the fireteam as soon as the 14th unique kill is secured.

NOTE: This achievement CAN be earned using mission replay... However, you must have a semi recent save file. Save files created prior to S2 are known to be buggy and this achievement may not pop there. See the Halo Infinite release notes around that time for more info.

NOTE #2: If you revert to a checkpoint for any reason, you must be careful to ensure you repeat any unique kills that were nullified by the revert. Kills obtained after that checkpoint but before the reset of course no longer count.

The following are the weapons/grenades required for this achievement. No other weapons, grenades, or plasma coils are required.

I've listed the weapons in the order they can be encountered in the campaign as well rarity of them present throughout the level. Remember, you can ping the map to spot any hidden weapons you may be looking for.

First available in scrap hangar at mission start
1. MA40 AR - Plentiful, default loadout and scavengeable
2. MK50 Sidekick - Plentiful, default loadout and scavengeable
3. M9 Frag Grenade - Plentiful, default loadout and scavengeable
4. Plasma Pistol - Plentiful, carried by grunts/jackals, scavengeable, and in weapon racks
5. BR75 - Only 2 available. The first one is hidden in a junk crate that is moved within the scrap hangar. The second is in the room with 2 Atriox holograms just before entering the bridge.
6. CQS48 Bulldog - Only 2 available. The first one is hidden on a suspended platform in the scrap hangar. The second is in the hallway after the elevator ride.

First available in the control room after leaving scrap hangar
7. Mangler - Plentiful, carried by brutes and on weapon racks

First available in Atriox's hologram room following the charging brute
8. Needler - Plentiful, carried by jackals and on weapon racks

First available in pod hangar before grappling to the elevator platform
9. Pulse Carbine - Plentiful, carried by brutes, scavengeable, and on weapon racks

First available in AR hologram room after the elevator
10. Spike Grenade - Plentiful, dropped by brutes and on weapon racks

First available in long multilevel hallway where the Boom Skull is found
11. Plasma Grenade - Plentiful, dropped by grunts and on weapon racks

First available in the hallway on the second floor leaving the prior hallway
12. Plasma Cannon - Only 1. Occasionally will not spawn due to a bug introduced in Season 3.

Available in the Warship Gbraakon's Bridge
13. Ravager - A few. Carried by the brute chieftain and on weapon racks

Available immediately after escaping the collapsing pod sequence on the platform under the crashing elevator
14. Hydra - Only 1. Hidden behind boxes on the left.

For most players this achievement will pop once the kill with the Hydra found near the end of the level is performed. However, with mission replay the earliest one can pop this achievement is when you encounter the plasma cannon if a Ravager and Hydra are brought into the level.

SKULL NOTE: This achievement is unlockable with any skulls active, including Bandana.

Surprisingly, this simple achievement is causing lots of confusion among players due to various myths about the requirements. So let's play Halo Infinite "Mix Things Up" MythBusters…

This achievement can be earned...

• ...in Mission Replay: Confirmed. However the save file must be semi-recent. Save files created prior to S2 can have issues resulting in some achievements not popping.

• ...using weapons carried in from Mission replay: Confirmed

• ...using weapon variants, such as the Striker Sidekick, MA40 Longshot, BR75 Breacher, Convergence Bulldog, Pursuit Hydra, Riven Mangler, Unbound Plasma Pistol, Pinpoint Needler, Rapidfire Pulse Carbine, or Ravager Rebound: Confirmed

• ...on any difficulty: Confirmed

• ...in co-op: Confirmed

• ...with melee attacks with the bladed weapons: Busted. The Mangler and Ravager killing blow must be a result of the weapon's projectile.

• ...from the lingering burn after a fully charged Ravager shot: Busted. The enemy must die from the impact of the Ravager's fired projectile for this kill to count.

• ...cumulatively across multiple playthroughs: Busted. All 14 kills must occur in a single playthrough of the mission Warship Gbraakon.

This achievement can glitch...

• ... when the Plasma turret fails to spawn: Confirmed. Known bug, level restart is required if this happens.

• ... by using the BR and/or Bulldog found at the beginning of the level: Busted. Reports that these two weapons don't count are FALSE.

• … using skulls including Bandana: Busted. This achievement will unlock when any combination of skulls are active.

This achievement requires…

• ...a deathless run: BustedThe achievement will still unlock if one dies during the run. However, if your death results in a revert to check point prior to a particular kill was earned that kill no longer counts and you must redo it.

• …a sole Spartan on the fireteam to get all 14 kills: Busted. All kills by the fireteam count toward this achievement.

• ...both a mounted AND a dismounted kill with the Plasma Turret: Busted. The kill can be secured mounted OR dismounted.

• ...a kill with the Dynamo grenade: Busted, this grenade does not typically appear on this level and thus is not required.

• ...a kill by throwing one of each Plasma Coil: Busted. Kills as a result of exploding Plasma Coils, thrown or not, have ZERO effect on this achievement.

• …using the Disruptor, VK78 Commando, M41 Spnkr, and the Heatwave when running with the Thunderstorm Skull enabled: Busted. These weapons are NOT required even if the Thunderstorm Skull is activated.

• ...landing a stick by the plasma/spike grenade: Busted. The kill counts as long as the enemy dies as a result of the explosion of the grenade, stick or not. Environmental kills from a chain reaction definitely don't count.

• ... a melee kill: Busted Melee kills, whether aided by the grapple or a bladed weapon are not required for this achievement.

To get the achievement, you must launch the first mission Warship Gbraakon and eliminate an enemy with each of the weapons and grenades available in the mission.

Here is the list of weapons to use:
- MA40 ASSAULT RIFLE
- MK50 SIDEKICK
- CQS48 BULLDOG
- BR75 COMBAT RIFLE
- PLASMA PISTOL
- MANGLER
- NEEDLER
- PULSE CARABINE
- FRAG GRENADE
- PLASMA GRENADE (attached and splash damage)
- SPIKE GRENADE (attached and splash damage)
- PLASMA CANNON
- RAVAGER
- HYDRA
- EXPLOSIVE COIL (an indirect explosion also counts)
- PLASMA COIL (an indirect explosion also counts)

Warning: if a Grognard dies following the explosion of his tank, the elimination does not count for the achievement.

Here is a video to help you:

Here's what I did to get that buggy achievement to work:
- I just replayed the mission on my 100 % save.
- I had the Bandana Skull active.
- Shoot the Grunts in the legs or lower body to not cause the explosion by their devices behind their heads.

1) Go to FOB or Outpost and get yourself the Ravager & the Hydra weapon.
2) Go into the Map menu and load the first Mission.
3) As soon as the Mission is loaded, all cutscenes have played out (skip them) and the game has saved, go into the map menu again and fast travel to "Armor of Reckoning" a little bit to the south of Outpost Tremonious.
4) Turn right and follow the muddy path upwards till you see the Plasma Cannon. Take it.
5) Open the map and fast travel back to the first mission. Now you should be at the start of the level with the plasma cannon in your hand and the ravager & hydra equipped.
(if you get the cannon first, it will despawn during the opening cutscenes)
6) Now just play the level carefully and kill every enemy with every weapon listed & it should pop 100 %.