I am starting over at Halo CE and am taking note of the toughest missions in Halo CE, Halo 2, Halo 3 and Halo 4. I just started but would be interested to know your personal top 5 hardest LEGENDARY missions. So far I know I will be adding Cairo Station from 2 to this list. I also am not looking forward to Halo 3’s Cortana mission. That will probably be 1st. 
Looking forward to reading your thoughts!
Hard to pick just one but I am thinking it will be a halo 2 mission.
Regret or Gravemind from Halo 2 are easily the hardest. At least Gravemind is fun though, Regret is just a pain because of Jackal Snipers and the final boss. My full top 5 list is:
Honorable Mentions:
All Halo 2 Missions
Assault on the Control Room Halo CE
Keyes Halo CE
Library Halo CE
All Halo Campaigns In Order of Difficulty:
As a person who has played all the campaigns on Legendary trust me when I say that none of the Halo 3 missions are too difficult. I consider The Ark, and The Covenant tougher than Cortana. I also consider Cairo Station and easier mission in Halo 2 because of the lack of Jackal Snipers.
Good luck
lol, while CE has its moments scattered about, Cairo Station really hits the ground hard with its Legendary setting. Mostly because there’s little one can do to avoid the fights where in the other levels, one can skip most of the fights (I spent High Charity running OVER the level 
… If H2 had more frequent checkpoints it could be a lot easier, however because it can spread them out so drastically, H2 can take the cake for those without the right knowledge.
Now if we were to not cheat the system and played the level as mostly intended (not level breaking)… Cairo Station, H2 and Gravemind, H2 pretty much tie for first for me.
I could note some rather difficult moments elsewhere, such as the long gondola section of Shutdown, H4 or the last long section before getting Cortana in her namesake level in H3… But those are only momentary hurdles where if one takes it one kill at a time, it’s more tedious than difficult. Cairo Station and Gravemind both have multiple sections where the hurt can just repeat itself over and over again for what seems like hours (but is really about 15-20min).
Most levels in H2 because checkpoints don’t always pop up when they’re supposed to. So often I’d get passed a hard point in a level and get killed shortly after and have to redo it all because the check point failed to pop up.
The library from CE, as it has unlimited spawns for flood.
> 2533274973373704;6:
> The library from CE, as it has unlimited spawns for flood.
http://halo.wikia.com/wiki/Unlimited_EnemiesThe Library isn’t on the list and as far as I remember, though there are seemingly inexhaustible moments of Flood in the Library, that feeling isn’t restricted to the Library and they’re just really deep Monster Closets that get closed if you push far enough, fast enough.
No body gonna mention Halo Wars? That game had some hard levels on legendary, namely Arcadia City and Shield World.
The Library is very easy, even on Legendary. Plenty of health packs, ammunition. The only problem with it is that it’s long and repetitive. So, boring.
Halo 3 isn’t bad. Always have a needler in your back pocket for Cortana and you’ll be okay. The hardest part for me was Tsavo Highway, fighting off the Brutes on foot, and then having to navigate up to the highway against choppers and wraiths.
CE is a cluster if you don’t know how to speed run. Truth and Reconciliation is a b*tch if you drop the sniper rifle, because ammo is scattered throughout the level. There are also a few tough spots on Assault on the Control Room and Two Betrayals.
Halo 2 is far and away the hardest. A total mess. If you can memorize the Jackal Snipers and make your shots, you should be okay to start out. But the overall uselessness of the sword against Brutes/Elites really sucks.
The Library was always annoying for me. It helps to know the Flood spawn locations.
> 2533274832967331;8:
> No body gonna mention Halo Wars? That game had some hard levels on legendary, namely Arcadia City and Shield World.
Yeah I always had my evacuation ships blow up on Arcadia which was very annoying. And the mission with the plasma tanks that you have to use. When I first played I only had a few marines and a warthog defending my base when the covenant game with so many troops and blew apart my base. I always keep a few tanks there now.
Ugh, Gravemind. -_-
> 2533274871369933;11:
> > 2533274832967331;8:
> > No body gonna mention Halo Wars? That game had some hard levels on legendary, namely Arcadia City and Shield World.
>
>
>
> Yeah I always had my evacuation ships blow up on Arcadia which was very annoying. And the mission with the plasma tanks that you have to use. When I first played I only had a few marines and a warthog defending my base when the covenant game with so many troops and blew apart my base. I always keep a few tanks there now.
Good ole Arcadia city…I hated that mission.
All you do is protect one ship with mass hornets and Forge.
Just remember to get Wolverines(forgot if accessible) or clear the ground forces and stock up on two turrets.
Putting the beneficial skulls on wouldn’t hurt either.
Also, wingman is a life saver.