Mass Effect Legendary Edition

This achievement is unlocked by beating any of the 3 games on Insanity after having already beaten one of them on Insanity.

I have heard of numerous people, myself included, who didn't get this achievement after finishing Mass Effect 2 on Insanity. If you have a save before the Saren fight in ME1 you can load that save and redo the Saren fight and it should pop sometime during the following sequence.

It is worth noting that a similar bug exists for Paramour II and the solution is the same - reload a save before traveling to Ilos in ME1 and after redoing the romance scene it should pop.

There is a TL;DR at the bottom since this is long-winded. However I recommend reading the entire thing, especially if you're struggling with Insanity on Mass Effect 2.

Intro:

Put aside everything you know from ME1; it won’t be of much use here—except for your imported character. If it’s been a while since you played ME2, I strongly recommend going through the prologue to reacquaint yourself with the controls and overall feel of the game. On the Insanity difficulty, every enemy has some form of defense—whether it’s Armor, Shields, or Barriers, or a combination of these. Your objective is to break through their defenses without getting yourself killed. Fortunately, each type of defense has its own weakness. Now, let me outline the build and provide you with a roadmap to success.

We're going to be playing Sentinel with the bonus power of Warp-Ammo. Our leveling path is this:

1) Focus solely on Tech Armor first. Don't even look at the other powers—even if you have a leftover point.
2) At Level 4 of Tech Armor, choose Assault Armor.
3) From there, focus solely on upgrading Defender.
4) At Level 4 of Defender, choose Guardian.
5) After that, Focus on Warp-Ammo (Heavy, not Squad), it's VERY effective against The Collectors.
6) It's your choice here, Overload or Warp. Since Warp-Ammo is good against Armor and Barriers, I opted for Overload against Shields.
7) Finally level up your Warp, you have to unlock Throw 2 to get it.

Squad:

Before the Collector Ship our squad will be Miranda (Overload and Warp) and Mordin (Incinerate). After the Collector Ship our squad will be Miranda (Overload and Warp) and whoever fits the mission, usually Garrus or Samara (after their Loyalty missions). This is because the leveling path I've outlined doesn't give you powers at first, so you'll be quarterbacking their powers. Your squad is pretty much useless in a gunfight, so keep them out of the enemy's line of sight and out of their reach. They're simply there so you can use their powers to chip away at enemy Defenses. For the Suicide Mission I went with Grunt and Garrus. They need their respective Heavy Ammo (Incendiary and Armor-Piercing) and Heavy Concussive Shot upgrades. This is because almost every enemy on the Collector Base has Barriers and/or Armor.

Play-Style:

This next section is a little wordy, but it's important to read if you don't understand how Tech Armor works. Your play-style heavily relies on your Tech Armor and the ability to instantly reactivate it when it’s destroyed. While Tech Armor lasts until it’s destroyed, it actually recharges like your standard Shields. Leveling up Defender next significantly reduces Tech Armor's long cooldown time. It’s important to note that the cooldown occurs while wearing your Tech Armor, allowing you to reactivate it instantly when it gets destroyed. Rather than providing an extra layer of protection, Tech Armor boosts your existing Shields. When your Tech Armor breaks, it emits a pulse that stuns and damages nearby enemies. Notably, starting from rank 3, using Tech Armor also resets squadmate cooldowns, enabling rapid-fire power combos with precise timing. So, when your Tech Armor breaks and you instantly reactivate it, your squad’s powers will be refreshed. This is especially advantageous when dealing with Praetorians. At level 4, opt for Assault Armor, which offers a wider knock-back radius, increased damage, and instantly recharges half of your normal shields which gives you some breathing room and time to reactivate the Tech Armor. The recurring mention of Tech Armor breaking underscores its importance throughout your play-through. You can play very aggressively with these steps:
1) Activate Tech Armor.
2) Stay in cover until cooldown finishes.
3) Aggressively move on the enemy.
4) Mag dump your SMG into someone's face with Warp-Ammo which will melt most protections away.
5) When the Teach Armor breaks reactivate it.
6) Repeat.
With the build order I've outlined, you shouldn't be scurrying around like a scared rat, taking damage and barely surviving. While you're not going to be invincible, you should be able to have a commanding presence on the battlefield with strong Tech Armor and fast cooldown times. This is also why it is very important to get anything that strengthens your Shields, reduces cooldowns, and makes your SMG more powerful (and more ammo).

Difficulty Spikes:

Now playing through the game is pretty straight-forward. However I've identified several "roadblocks" where the difficulty spikes. I'll break the game down into chapters: Freedom's Progress; Kasumi to Archangel; Horizon; Collector Ship; Reaper IFF; Suicide Mission. Pretty much any level with Collectors.

1) Road to Freedom's Progress:

Freedom's Progress is the last of the prologue missions, and is a good filter to see if you're ready to tackle the rest of the game on Insanity. This can be made a lot easier by importing your character from ME1 with a level as close to 60 as possible. Starting with a level 5 character if you imported a level 60 character from ME1, or level 3 if your ME1 character was between levels 50 and 59, can make a significant difference. Also, if you’ve previously completed ME2 with an imported character or have beaten the game twice, you’ll receive a 25% EXP bonus this time. Having the Rich Achievement from ME1 and any resources carried over from a previous ME2 play-through will give you a nice head start. Finally, if you've previously played ME2 and completed the loyalty missions, you should have access to bonus powers. Freedom's Progress itself is pretty straightforward. The mechdogs are annoying. The YMIR Mech at the end is the biggest challenge. Just keep the stack of crates between the two of you.

2) Road to Kasumi's loyalty mission and recruiting Archangel:

Do everything you can that doesn't involve on-the-ground combat. First go to the Citadel and Omega and get discounts at the stores and picking up things that your crew needs. Consider purchasing an SMG and Shield upgrade if you you have the money. Additionally, I recommend acquiring the Terminus Armor from Harrot’s Emporium, which provides a 10% increase in ammo and storm speed, along with a 15% boost to shields. Then I would go ahead and complete a few Firewalker missions for some EXP, you want to get as leveled as possible because your first combat mission is Kasumi's loyalty mission. Your goal here is to acquire the M-12 Locust SMG. Enhance it further with SMG upgrade and take advantage of the skill-point that has been automatically invested in Warp-Ammo. Be patient, the flying gunship at the end can be a pain. Kasumi’s mission may prove challenging, but with her abilities like Shadow Strike and Overload, you’ll manage. After that, recruit Mordin. Then you'll want to tackle the Archangel recruitment mission. Be prepared—the vitality bar for Archangel depletes rapidly, so consider it a speedrun. And don’t overlook the second SMG upgrade (grab it before crossing the bridge).

3) Road to Horizon:

After completing Kasumi’s loyalty mission and recruiting Mordin and Archangel, the game will ease up a little. The next challenge is Horizon, but with continued leveling up, it becomes manageable. You want to do get as much EXP and as many pertinent upgrades as possible before going to Horizon. Focus on improving your SMG and Shield first, followed by tech and biotic enhancements. Also get upgrades for whatever secondary weapon you are going to choose on The Collector ship (I recommend shotgun). You can find detailed information on abilities and upgrades (and their locations) in the game’s wiki. Horizon is your first taste of The Collectors, and it tastes bad. Your Warp-Ammo will be very helpful here. There's a Praetorian at the end of the level, but don't panic. Just play ring around the rosie with it. I stay just slightly out of its reach while shooting with my SMG. Warp-Ammo really chips away at it. Every time your Tech Armor breaks and you refresh it, your squadmates' powers also refresh, so take advantage of that. It'll take awhile, but he will be brought down eventually. There's plenty of ammo that respawns around the level, so don't be afraid to just keep magdumping it.

4) Road to The Collector ship:

The Collector ship sucks, there's no way around that. Especially the floating platforms and constantly being harassed by Harbinger. That's why before you take the call from the Illusive Man, you get as leveled up as possible, and get as many upgrades as you can. Hardened Shields would really help here. The floating platforms is the worst part, and it may take you a few times. For this specific level I brought Garrus and Thane because I wanted that firepower they provide. I also chose the shotgun as my secondary weapon (I bought the Geth shotgun on Omega). After almost smashing my controller, and ten attempts later, I realized that getting hyper aggressive while swapping between the shotgun and SMG really did the trick. I move right up to Harbinger, but get behind cover, then pop up and blast him in the head with a shotgun. You can pause the action using your power/weapon selection menu to move your crosshairs right onto his face and then unpause and blast him. There are a few more dicey battles with Harbinger along the way, but nothing too absurd. There's a Praetorian at the end of the level...again. This time he brought friends. Take care of the underlings first, then focus on the Praetorian. Same deal, ring around the rosie using the ramps. Order your squad off by the the blast doors so it doesn't focus on them. The last hurdle is a Husk bum-rush right before the exit.

5) Reaper IFF:

You shouldn't be starting this unless you are completely leveled up with all applicable upgrades and loyalty missions completed. Reaper IFF is a Husk nightmare. Grunt is a must, Samara is a good back up. Let Grunt roam free with an Incendiary shotgun, but micromanage Samara with a Mattock. This is a mission where you have to constantly retreat in an orderly fashion. Just tactically pause the combat to orient yourself, and retreat back up and down stairs as needed. Try to focus down the collective Husks' armor before outright killing individuals, your Tech Armor's pulse will kill unarmored ones, so don't despair if you get swarmed. In fact. In fact I've found it highly effective to just target their armor down completely with powers and bullets, and let them swarm me so my Tech Shield pulse kills them off, especially at the end of the level. (Just be sure there aren't any shielded ones in the mix because they can keep beating you, preventing you from reactivating your Tech Armor, and you'll die). Melee attacks on lone unarmored ones is also highly effective, and taking out unarmored Husks' legs with gunfire will kill them.

6) Suicide Mission:

You should already be familiar with what crew members are supposed to be assigned to which role. If you want to storm through the level, Grunt and Garrus both armed with Mattocks is a great choice. Both have the Concussive Shot ability, which greatly complements your Warp-Ammo when dealing with Barriers. Grunt with Heavy Incendiary ammo, Garrus with Heavy Armor-Piercing ammo, and you with Heavy Warp-Ammo will clown Harbinger when he decides to show his face. Kill off the final boss and there you have it.

Here are some general tips that I've learned along the way:

1) This isn't ME1, you have limited ammo. Even if you're fully stocked, keep a mental note of where extra clips are in case you need to fall back and resupply.
2) If you're stocked up on medigel, don't just take spare ones for the credits. Keep their location in mind in case you need to go back and get it.
3) Your squadmates are dumb and tend to go down fast, try to keep them behind you, and behind cover. If one goes down, try to push through the engagement without wasting any medigel.
4) Prioritize enemies that rush you over larger foes. Unlike in ME1, you don't always want to take down the biggest guy first. Husks/Abominations, Krogan, Geth Hunters, and dogs (Varren and FENRIS Mechs) need to be dealt with ASAP. Geth Primes are also something to take out ASAP.
5) Coordinate the moment when your Tech Armor breaks so that you can utilize your squadmates’ abilities before reactivating it, as this will reset their cooldowns. This comes in handy when retreating or fighting massive enemies.
6) When retreating, remain calm and avoid allowing the enemy to corner you. If you start getting overwhelmed, pause the action by accessing the power/weapon menu to assess your surroundings. Then, strategically move yourself and your squad from cover to cover.
7) Ensure your weapon magazine is fully loaded before emerging from cover to take a shot. There’s nothing more frustrating than stepping out of cover, lining up the perfect shot, only to fire a single bullet and then automatically going back into cover to reload.
8) If you see heavy ammo, that means something is about to kick off.
9) Keep two save files. One before the mission, and one during the mission. Just in case you get into a mission that's way over your head.

TL;DR:

Play as Sentinel with Warp-Ammo bonus. Get the Locust early. Focus on leveling up and maxing Tech Armor first, then Defender, then whatever feels right for you. Your squadmates are pretty much useless in a gunfight, so pick ones that have powers that can help you strip protection faster, and keep them out of the way. Make sure you get all applicable upgrades, especially shield and SMG ones. Enemies who rush you take priority, do not allow them to overrun you. Consider getting the shotgun as your secondary weapon and use it alongside melee attacks. Always have your Tech Shield up, always be ready to reactive it, and always have a safe spot in case you need to wait for the cooldown. Don't panic, you should be fluidly moving around confident in the ability to reapply your shield when it breaks. It will break a lot, it's meant to as part of the build. That doesn't mean just run into the enemy lines thinking that you're invincible. Also be gentle with the medigel, if a squadmember goes down, see if you can tough it out. Anyway, don't stress it, with this advice you should be able to get through the game on Insanity no problem. My accuracy is terrible, and I did it.