I'v beaten Legendary All Skulls On for every game in the MCC. Halo 3,ODST, Reach, and 4 are a breeze in comparison to CE and 2, since the skulls are relatively balanced.
Halo CE, and Halo 2 clearly were not intended to be played with all these Skulls, Halo CE didn't even Have skulls originally, so the ones added in anniversary makes the balance simply retarded. The main 2 pains in the ass are Foreign which makes it so you can't use Covenant weaponry so your just locked out of half the sandbox, and Recession which makes it so every round you fire costs double in your clip, this is basically famine but worse, and stacked with Famine so you get 1/4 of the ammo you should. This makes the Reload glitch when you swap a weapon while reloading and it finish reloading on the ground at no cost to your ammo reserve mandatory.
Thankfully the Grunt Funeral Skill which causes Grunts to Explode on Death, and the Boom Skill which makes explosions twice as big makes things more manageable.
The only real hard part of the whole thing is the first room when you get aboard the Truth and Reconciliation, since it's entirely luck based, Grunts, Jackals and Gold Sword Elites will spawn in the doors, and if too many Gold Elites Spawn due to the only having 2 shots for a sniper before reloading, you just don't have enough fire power to kill them, if their numbers are too big, you have to get lucky and have mostly grunts that will explode and kill the Elites.
Halo 2 isn't all that bad either since most of the levels are held together with ducktape, The first level Cairo Station is the hardest one since it's the least broken, but with enough effort you can force the Invincible AI Johnson to follow you though the level by blocking his pathing to go back to the start with Vending machines.
Regret would have been easy if I didn't fuck up the trick to get into the boss room before Regret spawns, by rocket jumping and then blocking the doors with ankle high podiums so elites can't get past the doors the spawn though, but instead I had to do it legit, and Regret with the Mythic Skull has so much health that some people don't even think it's possible to only punch him to death, you need to throw a gernade at the same time as boarding him so it slips past his shield for extra damage. It would have been faster to replay the entire level and do the trick right, then keep trying to do the boss legit.
Gravemind is the last tricky part since you need to learn how to do the prison skip glitch, in which you go down the grav lift to the prison with a brute perfectly on top of you, and then once the Prision loads in, you look up at him and alternate pressing Jump, Melee, Reload, so you can melee lunge cancel toward him and rise up the grav lift until you hit the loading zone, which will have the grav lift reverse and send you upward to the next part of the level. This Glitch is pretty much mandatory since due to the Whuppopotamus skull maxing out Enemy AI Awareness going down that grav lift to the prison will have an extremely high chance of you being killed before you can even hit the ground, and the result in a level restart since there is a checkpoint going down the grav lift, you can't even fuck up the Brute placement and then See if you'll survive going down the gravlift, you need to make it damn well sure you get it right before the checkpoint hits.
The rest of Halo CE and 2 is pretty fun since it involves Script breaking speedrun tricks, and getting on top of the level. like in the level The Oracle for whatever reason if you send the elevator up and the back down then get underneath it you will super bounce up though the loading zone, and
then your invincible for the rest of the level, you just have to make sure after cutting the cables you jump down the elevator shaft at the right time since there is no platform to take you down.