Beat the game. I'm going to divide the final mission into multiple parts though, since these things take a while to write and a lot goes on during the rest of the game.
As the fleets prepare to begin the final assault on Earth, Admiral Hackett pays a visit to the Normandy so he, Shepard, and Anderson (who is speaking to them via Quantum Entanglement Communicator) can discuss their battle plans.
The Reapers have closed the Citadel's arms, making it impossible for the Crucible to dock. Not all is lost though. The Reapers are emitting a teleportation beam between the Citadel and London so they can move their victims to the Citadel for their ascension into Reaperhood. The Sword Fleet will fight the Reapers in space so Hammer Team can make it to London, fight their way to the beam and open the Citadel's arms, whereupon Hammer Fleet will protect the Crucible until it docks and blows the Reapers to hell.
The Normandy and the absolutely massive Sword Fleet enter the Sol System and proceed to be on the losing end of a Curb-Stomp Battle with the Reapers. Joker manages to get the Normandy through the slaughter and STEEEVE!!!1 gets the Kodiak to London.
Before Hammer can land, Fail Shep needs to take out a Reaper Hades Cannon that is shooting down the Hammer shuttles. Shortly after the squad gets off the shuttle, tragedy strikes when the Reapers shoot down STEEEVE!!!!1's Kodiak and I learn that my stupid spelling of Steve was for nothing, as Shepard just shouts a non-Narmy "Cortez!" if he dies.
Fail Shep uses a Cain to bring down Hades Cannon, only to becomes surrounded by Reaper forces. After the squad fends off a few waves of Cannibals, they are bailed out by Male Hawke Big Ben Major Coats and Admiral Anderson, who bring them to Hammer's Forward Operations Base.
At the FOB, Fail Shep says his final farewells to James, EDI, and Liara. He also finds Primarch Victus with the turian forces. Victus informs him that after Wrex's "betrayal" and the Tuchanka bomb explosion, the krogan terminated their alliance with the turians. Palaven's only hope is the Crucible.
There's also a random turret sequence.
Fail Shep heads up to Anderson's briefing room to prepare for the final, final assault.
Death List (I realized I forgot to add Victus' son):
- Countless Mooks and civilians
- Jenkins (Squadmate, Plot)
- Nihlus (Plot)
- Fist
- Stirling
- Anoleis
- Gianna
- Ventralis
- Benezia (Plot)
- Rachni Queen
- Peak 15 Scientists
- Talitha
- Conrad
- Jeong
- Zhu's Hope Colonists
- Fai Dan (Plot)
- The Thorian (Plot)
- Shiala
- Tonn Actus (Mission)
- Wayne
- Toombs
- Kirrahe
- Menos Avot (Plot)
- Droyas (Plot)
- Ganto Imness
- Ashley (Squadmate, Love Interest)
- Saren (Plot)
- Sovereign (Plot)
- Pressly (Plot)
- Fail Shep (Plot, Resurrected)
- 20 Normandy Crewmen (Plot)
- Wilson (Squadmate, Plot)
- Prazza (Plot)
- Whitson
- Jaroth (Plot)
- Garm (Plot)
- Jentha (Plot)
- Tarak (Plot)
- Kuril (Plot)
- Jedore (Plot)
- Okeer (Plot)
- Daniel
- Abducted Horizon Colonists (Plot)
- Kal'Reeger
- Kureck (Mission)
- Aresh
- Niftu Cal
- Wasea (Mission)
- Nassana (Mission)
- Niket (Mission)
- Enyala (Mission)
- Weyrloc Guld (Mission)
- Maelon
- Rael'Zorah (Plot)
- Talid
- Legion (Squadmate, Sort of Resurrected)
- Thane (Squadmate)
- Garrus (Squadmate)
- The Original Crew of the Normandy SR-2, including:
- Kelly (Quasi-Love Interest)
- Gardner
- Ken and Gabby
- Jacob (Squadmate)
- Mordin (Squadmate)
- Grunt (Squadmate)
- Miranda (Squadmate)
- Tali (Squadmate)
- Collector General (Plot)
- Zaeed (Squadmate)
- Feron
- The Shadow Broker (Plot)
- The Boy (Plot)
- Primarch Fedorian (Plot)
- Dr. Eva (Plot)
- Aeian T'Goni
- Rana (Plot)
- Charr (Plot)
- Dagg (Mission)
- Wreav
- Eve
- Padok
- Valern
- Udina (Plot)
- Kaidan (Squadmate)
- Kahlee
- Tashya Porae (Plot)
- Rila (Mission)
- Samara (Squadmate)
- Falere
- Dorn'Hazt (Plot)
- Koris
- Legion (Plot)
- Gerrel
- Xen
- Danna
- Veetor
- Raan
- Wrex (Squadmate)
- Kurin (Plot)
- Talon 5 (Plot)
- Tarquin Victus
- Oriana
- Henry
- The Breeder Queen (Plot)
- Jack (Squadmate, Love Interest)
- Kai Lame (Plot)
- Steve Cortez