I've beaten every Legendary campaign solo with no skulls (and some of them I've beat multiple times). This guide contains a list of general tips for each Halo game that made my Legendary runs much easier. Note that this guide does contain some spoilers—if you haven't beaten all the games on lower difficulties, I don't recommend playing Legendary anyway. Also note that you do
not have to beat Reach or ODST to get this achievement, you only need to complete CE, 2, 3, and 4
Halo CE* The Sniper Rifle and Pistol can each kill a Hunter in one shot to their orange flesh (Bungie coded their flesh as their weak spot, so headshot weapons instakill Hunters). This makes them a joke as long as you have a precision weapon (this strategy only works in Halo CE though)
* An overcharged Plasma Pistol shot will instantly drain the shields of any Elite or Jackal, no matter their rank. Spamming the standard shot is also pretty good against Grunts. In the Covenant-only missions, you should be carrying a Plasma Pistol most of the time. Overcharged PP shots also instantly kill Sentinels
* The Shotgun is the single best weapon in the game. For the later missions where you're fighting both Covenant and Flood, I suggest carrying both a Shotgun and Plasma Pistol most of the time. The only thing the Shotgun can't kill is a Wraith
* If there are both Flood and Covenant/Sentinels in an area, usually they'll fight each other if you just hang back. Once the fighting ends, you can easily clean up whatever's left
* In Mission 3 (Truth & Rec), don't drop your Sniper under any circumstances
* During the Warthog run in the final mission (The Maw), when Cortana tells you to stop for Echo 419, you don't actually have to wait and watch her get shot down. You can just keep driving which will save about 20 seconds (on Legendary the countdown is 5 minutes instead of 6, so every second is vital)
* When you get to the final part of the Warthog run where you have to get to the Longsword on foot, you can actually use a Rocket Launcher to launch the Warthog over the barrels blocking its way. If you're about to run out of time, it's worth trying this
Halo 2* This is the hardest Halo game on Legendary, and unfortunately it involves a lot of RNG. This game is just utterly broken on Legendary, you basically need to treat it like it's a cover shooter. Marines and Grunts can actually survive more damage than you
* The Shotgun sucks now. In Flood levels, use the Energy Sword instead (bonus: the sword uses less energy against Flood and it can dismember them easily, preventing them from being revived)
* Against Covenant, the Plasma Pistol EMP + BR/Carbine headshot combo is still king. Also, dual-wielding a Magnum and Plasma Pistol is surprisingly effective; you can use the PP's overcharge and then immediately headshot with the Magnum without needing to swap weapons
* In the mission Metropolis after fighting through the tunnels, you'll eventually come to an open area with seemingly endless Jackal snipers. The snipers are not actually infinitely respawning, there's just an insane number of them (I think there are around 20). You just gotta be patient and keep killing them
* At the start of the mission Gravemind, if a Brute goes berserk and starts charging at you, you can jump onto one of the pedestals in the middle of the room and he won't be able to reach you
* In the final mission, if you shoot off the wings of a Banshee, you can fly it into the final area where you fight Tartarus. It makes things way easier. If you don't use this glitch, then you're gonna have to spend 10-15 minutes wearing him down with dual Plasma Rifles
* In general, it's usually better to give power weapons to Marines if you have any with you because they have unlimited ammo and surprisingly good aim. A group of Marines with Sniper or Beam Rifles can make certain encounters much easier. Also, if you give a Marine a half-empty weapon, it's possible for them to basically give you free ammo by reloading the gun for you
* In a pinch, dual Needlers can work pretty well against Brutes because they have no shields (I used that tactic a lot in the first section of Gravemind)
Halo 3* Thankfully H3 is a lot more balanced than H2. If you can make it through H2 on Legendary, you should be able to handle every other game
* The Assault Rifle and Plasma Rifle aren't good at killing because they can't headshot, but they're actually a pretty decent medium-range shield/armor breaker. What I liked doing was burst-firing the AR or PR to break Brute shields/armor from a distance and then finishing them off with a BR headshot
* Dual plasma rifles can melt flood combat forms pretty quickly, give it a try
* Bladed Brute weapons (like the Brute Shot or Spiker) are slightly more effective at dismembering flood corpses than normal weapon melees. Usually normal melees work fine though, melee attacks are way better against the flood than in CE or H2
* The Needler is really good against those annoying ranged Flood forms that shoot spikes at you. Also, the Energy sword will kill the giant tank forms in one swing
* In the final level, before you enter the control room where you fight Spark, make sure you destroy any auto-turrets that you deployed. After Spark's boss fight, your own auto-turrets will become hostile
* In the mission Tsavo Highway, almost every single fight is skippable. It's possible with enough luck to speedrun the mission just by driving past everything
* When Arbiter gets knocked out, he'll usually pick up the closest weapon when he comes back to life. You can exploit this by dropping a power weapon near him when he gets KOed
Halo 4* Halo 4 on Legendary isn't that hard in my experience, it's just tedious. Most weapons have had their ammo counts significantly nerfed, so you will probably have to spend a lot of time looking for new weapons. In most cases, the optimal strategy is going to be picking off everything with a Light Rifle from a distance
* If you see a Knight point his arm at you and he doesn't throw a grenade, it means he's about to teleport towards you and try to melee you (on Legendary this is usually an instant kill if you don't back away in time)
* Watchers take first priority over every other enemy because of their ability to revive dead Knights, catch grenades and create shields in front of other enemies. On Legendary it usually takes 5 shots from most precision weapons or 1 shot from snipers to kill a Watcher
* Watchers tend to start flying around like crazy if you damage them, but they always seem to prioritize reviving recently killed Knights. They have to stay motionless for several seconds to revive a Knight. If you're prepared to kill it quickly, using dead Knights to "bait" Watchers into staying still can be an effective strategy
* At the start of the second mission, you can find a Sniper Rifle near the top of the crashed Forward Unto Dawn. There's also a SAW lying in the rubble somewhere too
* Knights regenerate their shields significantly faster than you or Elites do. Specifically a Knight's shields start recharging after about 4 seconds of taking no damage. If you break a Knight's shield and they teleport away, it's total BS but you will probably not find them in time, and chasing could get you killed
There's probably some stuff I'm forgetting but I hope these tips are useful. If you need help, feel free to leave a comment. If you need a detailed walkthrough for a specific mission, I highly recommend Hokiebird428's Legendary walkthroughs (
https://www.youtube.com/@Hokiebird428/playlists)