Extended Cut | Mass Effect 3 Wiki

Cutscenes

• Depending on the player's Effective Military Strength score, during the final rush to the beam, you will see Shepard's Companions either being incinerated or evacuated to the Normandy after being critically wounded.
• If the Effective Military Strength is low, the crucible and the shield fleet are being attacked as the Crucible docks with the Citadel.
• Hackett is noticed that someone, has reached the beam.
• When Commander Shepard is making the final choice, instead of Joker being shown in the flashback, a character who died will be shown.
• The last flashback now is about the Commander's love interest, and no longer about Ashley Williams, Kaidan Alenko or Liara T'Soni.
• Commander Shepard being violently launched into the Citadel Tunnel.
• When the Crucible reaches firing status, Admiral Hackett orders the surviving allied fleets to evacuate from planet Earth's orbit. This leads to Joker refusing the order until a surviving Companion, convinces him to leave. The Normandy barely manages to escape the system seconds before the Crucible fires. This explains why the Normandy was caught in the energy wave while still in transit.
• Two human Soldiers are shown being overwhelmed by Husks on Earth. Depending on the final choice, what the energy of the Crucible does to them. If you selected destroy, the Husks are vaporized, they retreat if you selected control, or they stop attacking if you selected synthesis.
• When the Crucible's energy interacts with the Charon Relay, the relay's core is shown breaking up. However, the rest of the relay remains intact, and you will see the mass relay being repaired in later scenes. If you have a low Effective Military Score and choose either Destroy or Control, the relay explodes.
• After the Crucible's energy wave hits the Normandy. the consoles and engines will be shown exploding depending on the level of Effective Military Strength. If low, they will be shown exploding, and if high, they won't explode.
• There are scenes showing victories against the Reapers on Palaven, Tuchanka and Thessia if you have a High Effective Military Rating.
• The narration of the ending depends on Commander Shepard's final choice. If you choose destroy, Admiral Hackett narrates it, if you inclined your decision towards Synthesis instead, EDI takes the role of the narrator. Finally, if you decided to pursue the control ending, Commander Shepard as the new Reaper master narrates it.
• Aftermath of various species will be shown. These include Humans, Quarians, Geth and Krogan. The aftermath of the surviving Companions is also shown.
• The Normandy is seen undergoing maintenance or leaving the planet it had crashed on previously.
• You will see the surviving members placing Commander Shepard's name onto the memorial wall. If the destroy ending was chosen and the player has a high enough Effective Military Strength rating, Shepard's name is not shown being placed on the wall. 

Dialogues

• The Catalyst's original dialogue has been altered, and Commander Shepard can now learn more regarding the Reapers origins and the Crucible's abilities.
• There is a fourth option provided to the player as an additional ending to the original three. You can now refuse to activate the Crucible, either through a dialogue choice or by shooting at the Catalyst. This allows the Reaper to complete their purge successfully. 
• If you choose to not activate the Crucible, you will be treated to two new unique cutscenes. One of them shows a Liara's time capsule on an unknown planet, while you hear a recording of her explaining that the capsule contains a record of her generation's war against the Reapers and information regarding on how to stop them.
  The second one, after the credits, shows an alternate Stargazer scene. A child and a female of an unknown species refer to how the previous cycle's experience allowed them to achieve peace.

General Fixes

• The required Effective Military Strength to achieve all possible Endings has been reduced from 4000 to 3100.
• The screen after the credits has been changed to show a message of thanks from BioWare.
• Ambient dialogue on the Normandy SR-2 between Garrus Vakarian/ Tali'Zorah vas Normandy and Kenneth Donnelly/Gabriella Daniels.