Halo 5: Guardians

In Osiris, use the squad command system - aim at an enemy, objective or vehicle and press the command button (up on the d-pad by default) to order your AI Spartans. Issue a few commands during the mission and it pops. It usually triggers through normal play; if it hasn't, deliberately order a teammate onto a target.

Unmissable - the opening mission. Best practice for 100%: play the entire campaign on Legendary in co-op. A single Legendary clear stacks Legacy, Heroes Rise and Forging a Legend, and a full fireteam of four makes Legendary far more forgiving thanks to revives.

Any one of the 117 Intel files. You'll trip over one early - claim it and this pops on the way to Hunt the Truth. Like Skulls, Intel persists across replays, so nothing here is missable.

Unmissable story progression - pops the moment you finish the mission. Nothing to chase.

Change your Emblem in the Spartan Hub - pick any new emblem or colours and confirm.

Forced story unlock. Just complete the mission; nothing missable.

Unmissable - completes as you finish the mission.

Unmissable story progression. Nothing to do but play through.

Forced unlock on completing the mission.

Unmissable story progression - pops on completion.

In the Spartan Hub (the customisation menu), change any piece of your Spartan's armour - swap a helmet or armour set and confirm. Ten seconds in the menus. Grab Make Your Mark and Raise Your Banner in the same visit.

Some enemies in Unconfirmed have shields or armour that regenerate if you stop shooting them. Damage one (a shielded Elite works well), back off and let its armour visibly restore, then kill it - the killing blow has to land after the armour has come back. Strip an Elite's shield, break contact until it recharges, then finish it off.

Forced story unlock. Complete the mission and it's yours.

Unmissable, pops on completion.

Forced story unlock.

Unmissable - completes as you finish the mission.

Forced story unlock, nothing to chase.

Change your Service Tag (the 2-4 character ID) in the Spartan Hub. Type anything different and save.

Unmissable. This is the big Scorpion/vehicle mission, so it's also where you'll grab the tank challenges Tank Still Beats Everything and Rolling Thunder - see their notes.

Open a Gold REQ Pack from the REQ store. Gold packs are the priciest - earn REQ Points by playing Warzone/Arena (and clearing commendations), save up, then buy and open one Gold pack. Purely a matter of grinding enough RP; the opening itself happens in the menu.

Unmissable story progression near the end.

The final mission - completing it beats the game, so this is your story-complete unlock. Whatever difficulty you clear on grants that tier (Legacy at minimum).

Complete 5 matchmade Slayer games - the easiest of the Arena-mode achievements since Slayer is always populated. Play 5 to completion.

In Warzone or Firefight, call in a REQ that costs 5 or more Energy - a higher-tier requisition like a strong power weapon, a vehicle or good armour. Build up your REQ Energy level during the match, then call something in that costs 5+. Any decent vehicle qualifies once your energy is high enough.

Complete 3 matchmade Warzone games (the big 12v12 mode). You'll do this naturally while chasing REQ points and the other Warzone achievements - just finish 3.

You'll get this simply for finishing the campaign - Normal is the floor and any clear grants it. No reason to play Normal specifically; go straight for Heroes Rise/Forging a Legend on Legendary and this stacks underneath.

Land the killing blow on a Legendary-tier boss in Warzone (the tougher named bosses at the boss sites). Get to a boss as its health drops and snatch the last hit - a power weapon helps you snipe it amid the scrum. Partly luck with 23 other players also shooting it.

Qualify for a Competitive Skill Rating by completing your 10 placement matches in a ranked Arena playlist. Just play out all 10 placements in any ranked mode - you don't need to rank highly, only to finish placements and be assigned a CSR.

In Warzone Firefight, land the takedown on a Mythic boss (the hardest boss tier, usually the final-round objective). Coordinate with your team to focus it and try to snatch the last hit. You'll get chances on the boss-rush final rounds of most matches.

Complete 5 matchmade games of Breakout (the round-based Arena mode). Win or lose, finishing them counts - just queue Breakout and play 5 to the end.

Any one of the game's 13 Skulls. The first few are easy pick-ups off the critical path - claim one and this pops on your way to Gravelord. Nothing missable; Skulls persist across mission replays.

Complete 5 matchmade Capture the Flag games in Arena. No need to win - play 5 through to the finish. One evening of CTF.

Win a Warzone match on each of the three launch maps - Raid on Apex 7, Escape from A.R.C. and March on Stormbreak. You need wins, not just completions, so allow a few games per map. Play until you've a victory on all three.

Complete 5 matchmade Strongholds games. Queue the Strongholds playlist and finish 5; results don't matter.

Successfully complete 5 Warzone Firefight matches (the free PvE horde mode). "Successfully" means your team clears all the rounds, so play with a competent team and see it through. Five wins.

Just one mission finished in co-op on Heroic or higher. You'll get it on the way to All for One the moment your first co-op Heroic mission ends.

Complete a Warzone Firefight match on 6 different maps. Just keep playing through the Firefight map rotation until you've cleared six distinct maps - it tracks automatically. Overlaps with Not Your First Rodeo.

Enemy Lines has you assault the Kraken (the giant Covenant walker), whose turrets you'd normally blow up. Finish the mission without destroying a single one - board and progress via the objective route, and simply don't shoot the turrets off. Any difficulty; just be disciplined about your targets. You'll finish the mission with the scripted Emergency Boarding Procedures escape.

Spectate a match - the easiest way is to set up a Custom Game and enter the spectator slot, or watch in a custom lobby. Quick and free; pair it with Gamemaster in the same custom game session.

A Heroic clear of every mission, granted automatically by a Legendary one - so just do Forging a Legend and this comes with it. In co-op with a decent fireteam, Legendary itself isn't bad.

Go into Custom Games, tweak any setting, and save it as a custom variant. No need to play it - just create and save one. Do Benchwarmer while you're in the custom lobby.

Score Attack is the scored campaign mode from the main menu. 10,000 points is trivial - you'll pass it within the first minute of almost any mission. You'll get this the moment you start playing Score Attack properly. All five Score Attack achievements stack in one good co-op run - see Party Hearty.

Every mission on Legendary. Far easier in co-op (up to four) - revives mean one death doesn't restart the encounter. Stacks Heroes Rise and Legacy beneath it. The solo version is the separate, much harder Lone Wolf.

A scripted moment in the Blue Team mission: rather than killing the Hunters where you first meet them (the lab), flee - leave the room and progress toward the hangar, where the game has you fight them properly. Don't finish them in the lab; run, and engage them later in the hangar. Any difficulty.

The hardest achievement in the game: every mission on Legendary entirely solo, no co-op revives. Do it last, once you know the encounters and where the power weapons and Prometheans spawn. Play patient - lean on cover, Smart-Link and precision kills, and don't be shy about reverting to the last checkpoint rather than burning through on a bad push. If you did Legendary in co-op for Forging a Legend first, you'll already know the routes.

Every mission completed in co-op on Heroic or higher - so a Heroic/Legendary co-op run for Heroes Rise covers it. You need at least one other player joined for the whole campaign, via matchmaking or a friend. Pairs with One for All.

Finish Mission 13 (Reclamation) on Legendary without losing your Scorpion. On Legendary the tank dies fast, so play cautious: hang back, break line of sight to avoid sustained fire, kill Wraiths and Banshees at range before they focus you, and hop out to clear infantry on foot rather than soaking hits. If it's about to blow, bail and let the heat off it. A co-op partner can draw aggro. The trickiest campaign challenge after Lone Wolf.

Reunion gives you a Phaeton to fly across a canyon - instead, cross it on the ground the whole way, on Heroic. Skip the aircraft and traverse manually. Slower and riskier on Heroic, so clear enemies methodically as you go; a lower-difficulty run won't count.

Complete Glassed without any player using Smart-Link (the aim-down-sights zoom) - hip-fire only, the whole mission. Just never press the zoom/ADS button. Note the check covers all players, so in co-op everyone must abstain - solo is far safer. Do it on a low difficulty so hip-firing isn't punishing, and pair it with Going the Distance (no vehicle) on the same run.

Beat a mission's par time in Score Attack - finish faster than the target shown. Pick a short mission, skip optional fights, and rush the objective. This wants speed, so it pulls against the high-score achievements (which want you to linger) - easiest on its own quick run.

Turn on three or more Skulls (the gameplay modifiers from the mission-select screen, not the collectibles), set Heroic, and finish any mission. Pick harmless ones - Thunderstorm, Cowbell, Grunt Birthday Party, Iron and the like don't make it meaningfully harder - and run the shortest mission. Nothing to it once they're toggled.

Complete the Glassed mission without ever entering a vehicle. Glassed hands you Warthogs and Mongooses to speed through - just travel the whole way on foot. Do it on a low difficulty to make the slog safer, and watch you don't get auto-seated as a passenger in a co-op partner's Warthog. Pairs neatly with Shoot from the Hip (no Smart-Link) on the same run.

All 13 Skulls, spread across the 15 missions. They persist across replays so there's zero missable pressure - mop them up from mission select with a locations guide. A few sit behind awkward jumps or a hidden switch nearby, so a video helps for those. Grants Gravedigger along the way.

Swords of Sanghelios is full of destructible walls and floor panels. Destroy 10 of them across the mission - Ground Pound is the reliable tool for breakable floors, and Spartan Charge or explosives handle the cracked walls. They're common in the temple areas, so ten adds up fast if you deliberately smash through things rather than around them.

All 117 Intel files across the 15 missions. Like the Skulls they persist across replays, so nothing is missable - clean them up from mission select with a locations guide. This is the single biggest collectible chore in the game, but none of it is hard.

Same exterior power cores as Double Stuff, in Guardians on Heroic - but this one must be destroyed with a Ground Pound specifically. Get above a core, charge the Ground Pound in the air and slam down onto it. Do this while you're lining up Double Stuff and bag both together.

During the Kraken finale in Enemy Lines, as it goes down there's a scripted escape - a Spartan flies a Phaeton past and you leap onto it. Follow the bail-out prompt and jump toward the Phaeton at the right moment. In co-op a teammate can be the one flying it.

Complete Evacuation in under 18 minutes without dying, on Heroic. It's a defence-heavy mission, so 18 minutes is generous if you push objectives promptly rather than dawdling between waves. Going down fails the no-death clause, so play safe. Try to keep all six miners alive for Savior on the same run.

Mission 13 (Reclamation) is the big vehicle battle. You need four different vehicle types being operated at the same time - realistically a 4-player co-op run where each Spartan grabs a different vehicle (Scorpion, Wraith, Ghost, Warthog/Mongoose) simultaneously in the open battlefield. Solo you'd be relying on AI teammates crewing vehicles alongside you, so co-op is far cleaner. On Heroic, though the difficulty isn't the hard part here.

In the Battle of Sunaion, you need one Ground Pound that both kills a Grunt and smashes a grate. There are grated walkways over the water with Grunts on them - get above one, charge the Ground Pound in the air (hold the crouch/clamber button) and aim it at a Grunt actually stood on a grate. The slam kills it and breaks the grate together. Line one up properly and it's easy.

During the elevator defence in Evacuation, six miners can be killed by the incoming Covenant - you need all six alive when the sequence ends, on Heroic. Hold an overwatch spot, prioritise anything rushing the platform (Grunts and Elites pushing in), and answer every Phantom drop fast. A power weapon or turret lets you thin waves before they reach the civilians. Doable on the same run as the timed Fire Drill.

Co-op: in the Unconfirmed mission, you and a teammate share a vehicle (one drives, one guns) and rack up 30 kills together from it. Grab a Warthog or Gungoose with a partner and mow down the Covenant across the mission's open stretches. Needs a second player crewing the vehicle with you - hence co-op.

Co-op required. In a Blue Team mission, you and a teammate each land an assassination (the from-behind melee animation) on an Elite at the same time. Sneak behind an Elite each, count down over comms, and trigger the assassinate together. Easiest at an early encounter with two Elites close together, on a low difficulty.

In Score Attack, hit 50,000 points with a Skull multiplier of x2 or higher active. Turn on a scoring Skull before you start (the ones that boost your multiplier), then rack up 50k over a mission - easy. Comes on the stacked run in Party Hearty.

Co-op required. Swords of Sanghelios has two Mantis walkers - you and a partner each pilot one, both active at once, through that section on Heroic. Grab a Mantis each and roll through the battle together. Solo you can only ever crew one, which is why it needs co-op.

500,000 points in a single Score Attack mission. Pick a long, enemy-dense mission, keep your scoring chain alive (dying resets your multiplier) and clear everything. Falls out of the stacked co-op run described in Party Hearty.

In the Guardians mission you destroy exterior power cores - here two must go down at the same time, on Heroic. Damage both to breaking point, then trigger the final hit on each within the same moment. Co-op makes the timing trivial (one player per core); solo, damage one and immediately finish the second. Set up Icy Cool on the same cores and grab both together.

At the Covenant camp in Reunion a Phantom dropship lingers - destroy it, on Heroic. Grab a power weapon (Fuel Rod, Rockets, or a turret) or commandeer a Banshee/Wraith and focus it down before it flies off. If it escapes, revert to the last checkpoint and try again.

In Osiris there's a friendly Elite General who pushes up a hill - keep him alive and support his charge, on Heroic. Clear the Covenant and Prometheans ahead of him and don't let him get swarmed. Stick close and shoot anything targeting him, and he'll make it up.

During the Battle of Sunaion you fight Hunters on platforms above the sea. Knock two of them off the edge into the water. A Ground Pound, Spartan Charge, or an explosive near a ledge staggers or launches them - position yourself so the Hunter is between you and the drop, then shove it over. Two of them, any difficulty.

Finish The Breaking on Legendary without your whole fireteam wiping at once. Your AI Blue Team members count as the fireteam, so keep at least one of them up through the multi-Warden fight and you're fine even if you personally go down - a full team wipe is what fails it. Grab Prison Break on the same run.

The Breaking pits you against multiple Warden Eternal bosses at once - you need two of them to die at (near) the same moment, on Heroic. Whittle both down to a sliver, then finish them within a beat of each other; a Spartan Charge or heavy weapon into their glowing back panel does it. Much easier in co-op where you each drop one on a count, though it doesn't require co-op. Do it on the same run as Harbinger if you're on Legendary.