Don't let the Reapers get close
Made from the reanimated tissue of other races, Reapers are kind of like the undead of the Mass Effect galaxy. Dont let them close in and overwhelm you, bring a Soldier or a Vanguard who can put down enemies fast. An Adepts Singularity is essential for corralling oncoming Husks and Cannibals. Both Brutes and Banshees have an instant kill at melee range, make sure your biotics are wearing them down with Warp combos.
If you can, take out Marauders first, before they can power up their allies. They have shields and tend to stay further back, an Engineer with Overload or Energy Drain and a long range weapon is well prepared to deal with them.
Most Reaper forces will close in and force you to leave cover. Ravagers take advantage of this by pounding you with their long-range guns. Keep an eye out for their targeting lasers, roll or seek cover as soon as you see them. A Ravagers armor is susceptible to fire damage or biotics. Soldiers should burst the Ravagers front sack and target the fleshy green area behind it.
A Krogan Soldier is the perfect ally against Reapers, he can torch multiple foes with his Inferno Grenade and rip Husks apart at melee range. An Asari with Stasis Bubble is great for crowd control. Bring an Engineer for Incinerate, plus Combat Drone and Decoy will help take the pressure of your team. The Quarian Engineers Sentry Turret will soften Reaper forces and slow their advance, especially with Rank 5 Cryo Ammo.
Use Incendiary Ammo to melt Reaper armor, and the burning damage is useful for hard to hit Husks and unarmored Cannibals. Cryo Ammo will stop charging Reapers in their tracks.
Disrupting the Geth
The Geth are a purely synthetic race that rely heavily on shields. An Engineer with Overload or Energy Drain is essential, and it doesnt hurt if someone has a sniper rifle to target Geth Pyro fuel tanks. Geth forces have no one hit kills so Vanguards are free to charge, but beware of the Geth Primes rockets, which can stagger you.
A Quarian Infiltrator can really wreck havoc with Sabotage, turning Geth against each other, especially if you spec with Duration, Explosive Hack and Berserk. Use it on a powerful enemy, like a Geth Prime or Pyro. A Salarian Infiltrator can drain enemy shields, and use Proximity Mines to stop cloaked Geth Hunters from sneaking up on the team.
Disruptor Ammo ruins shields, making it perfect against Geth.
