Compared to his predecessor, Mass Effect 2 Insanity mode is child play, if you manage to bet the first game on Insanity then you probably don't even need this guide, however i strongly recommend you to stay until the end, since I will be telling you how to make sure all your squadmates and crew survives the ''Suicide Mission''. If you are looking for the Suicide Mission guide then jump to the end of this page. Before I start, be sure to watch out since this guide will contain major spoilers, if this is your first time playing then quickly leaves this guide, if not, then let's do it.
The Beggining
If you complete Mass Effect 1 then you can import your character, you will get credits and keep your level, you already will have your class powers which will make your fights easy, especially early on game. No need to worry, in Mass Effect 2 enimies don't spawn Immnunity, but they will have shield, barrier and armor, or in case of bosses all three of them, it may sound intimidating, but don't worry those proctetions can be overcome with ease. I can sound like a biotic zealot, but once more i strongly recommend a biotic class, adept is a strong class, but i ask to give Vanguard a chance, this class got one of the most strong abilities, ''Charge'' is your ultimate BFF, once fully completed, you can charge into a enemy and recover your barrier, a vanguard with cooldown abilities will be almost unkillable since at each charge you recover your barrier. Assault Mastery specialization you want to pick is Champion, which grants cooldown reduction in all abilities, if Bonus Powers are available then choose Warp Ammo, in it final upgrade you got a major damage bonus for your weapons.
Build
I will be using Vanguard as example, but every class can be dangerous. In every class your focus is to destroy your enimies, doesn't matter if you take things in front lines or spawn debuff in your enimies. As a Vanguard you need to priotize cooldown reduction and power damage, different that the first game, in ME2 you can use a lot of weapons in every class. A Assault Rifle is necessary, M-96 Mattock is your best pick, she got fast firerate, a insane damage with high accuracy, but she can't be your only weapon, Sniper Rifles are cool, but you won't be using them as a Vanguard, instead pick a shotgun , Geth Plasma Shotgun is the best one, since she can fire at long ranges and charge up the shot, also pick M-12 Locust a SMG who is useful against biotic barries and in mid to long ranges fights, for your heavy pistol M-5 Phalanx is the best one, with rapid firing, excelent accuracy and perfect damage, and finally the most punisher weapon, M-920 Cain fires a nuke, pretty much like the Fatman form the Fallout Franchise, and her damage can oneshot even on high difficult, but only use her against tough bosses, against regular enemies your best pick would be ML-77 Missiler Launcher, her damage is decent and has fast firerate that follow the target, only use Heavy Weapons against bosses or tough enemies, like Scion. Basically you want to level up the ''Charge'' skill the fastest you can, she will be your primally damage , escape and barrier restoration.
Combat Simulation
Start a fight by activating Warp Ammo, open fire with your Assault Rifle, once the ammo is depleted change to your mid to long range weapons, if the enemy are trying to get closer then is time to Charge plus shotgun combo , never stop using Charge or you will die, always retreat when necessary and take cover , dont' try to take all enemies head on, especially against targets with protections. Mass Effect 2 introduces a new mechanic called combo, be sure to use Warp before Charge to trigger a Biotic Explosion for extra damage, Samara or Morinth's Reave can also primer Charge to the Explosion, exploit this mechanic in every opportunity, if you can't make it, then use your teammates power, a early example is Jacob's Pull then Miranda's Warp. One more tip in combat is to watch out for weapons strongest points for each protection, usually rapid firing weapons, like Locust are effective against biotic barries, also don't forget that your squadmates can be deadly as you, so do not underestimed they. Watch out for the gank, almost start with the weakest enemies, being surrender is more deadly that a full barrier enemy, usually you will get surrender in collectors related missions, ignore the scions or Harbinger, first destroy the drones, then Harbinger and Scions, if a Praetorian is on game, then running is essential, It will charge against you, and if gets to close it would be impossible to escape it melee attack, just run.
Squadmates
Since I enjoy most of the characters i try to diverify my party at each mission, Miranda and Samara are the best ones since them can create explosions by themselves. Miranda is your primer character, she can iniciate or detonate the explosions, she does well with others biotics, like Jack, Thane, Jacob, Samara or Morinth. Basically you want a biotic only team, also consider bring Grunt since he can be invincible with ''Krogan Warlord'' and ''Fortification'', also make sure to pick ''Squad Incendiary Ammo'' useful for the other teammate, despite being recruited late game, Legion has exclusive acess to the powerful ''Widow'' rifle, which can oneshot some enimies , combine this with Incendiary Ammo and you got a heavy damager. Avoid bring characters like Tali in missions with barrier only enemies, since she doesn't have any power useful against it. In Collector related missions, characters like Miranda, Mordin and Samara are essential, while dealing with geth Zaeed, Tali, Garrus or Kasumi. Zaeed, Thane, Grunt and Garrus has acess to special ammo , make sure the pick the bonus that share the effects with the entire squad. Miranda is useful against all types of enemies thanks to her skills and ''Cerberus Leader'', so she takes the spot for the strongest teammate.
Biotic Combos
In Mass Effect 2 the combos are few, but still there, first you have the Biotic Primers powers which are :
Pull (Jack, Jacob, Morinth , Samara )
Singularity
Slam (Miranda)
Then you need to activate one of the powers below to sucessful trigger a explosion :
Shockwave (Jack)
Throw ( Morinth, Samara, Thane )
Warp (Thane, Miranda)
How To Make Your Squad Survive The Suicide Mission
To avoid the members dying before the quest herself, you need to buy some upgrades for the Normandy, so before starting the mission make sure to head into the Science Lab (Where Mordin stays) and buy all avalaible upgrades, ''Sillaris Armor'' , ''Cyclonic Shields'' and ''Thanix Cannon'' are the names you after, if they aren't on the list, so make sure to talk with your squad and explore each dialogue option, by buying all three upgrades your team is making into the Collector Base. But, another part arrives, now you need to plan the assault, and if you choose the wrong teamates, or if they aren't loyal, they will die, so pay attention below and pick the rights one, don't try to choose others, or somebody will die. The most important thing is to complete all squad members loyal mission, or some of they will die no matter the choices.
The Base
The Vent Specialist : Tali, Kasumi or Legion (Dies If Not Loyal)
Second Fireteam Leader : Miranda, Garrus or Jacob (Dies if he/she isn't loyal or you choose somebody else)
The Long Walk
Biotic Specialist : Samara, Jack or Morinth (If not loyal or you choose somebody else she/he will not be able to maintain the barrier and a random squad member will die.
The Escort
Escort Leader : Any party member. (If you don't choose somebody to escort the crew, then they will die, also if the escort party member isn't loyal then he/she will die.
Hold The Line
Make sure to bring only loyal party members into the final battle or they will die, members like Grunt, Zaaed, Thane, Samara , Garrus, Miranda and Morinth should be left to cover you, avoid to leave members like Mordin, Kasumi, Jack or Tali since there is a chance they will die holding the line, try to balance the team, by leaving three loyal ''strong'' members to cover you.