At this point, you’ll take part in one of several endings.
All endings are dependent on two major factors: the total value of all War Assets collected and the Readiness Rating percentage.
There are hundreds of variables that determine what War Assets you ultimately end up with.
We cannot tell you exactly how to get each one, since getting them depends on decisions made in Mass Effect 3, decisions made within imported saves, game time, and even online connectivity.
A number of War Assets also change the scenes you witness over the course of the final battle.
Readiness Rating determines the Effective Military Strength of all War Assets.
The lowest it can be is 50 percent. A good method of raising this rating is through multiplayer, and BioWare will be providing additional methods to increase readiness outside of the game.
However, even at the lowest percentage possible, all endings are within reach if you do what you can to bring as many War Assets to the final battle.
Even players without access to online multiplayer are capable of getting the best endings. After beating the game once, starting a New Game Plus opens up new possibilities.
A secret ending is also available to players who complete the game a second time.
In the interest of keeping this guide somewhat spoiler-free, we’ve eliminated screenshots for each ending.
The brief description should be spoiler enough; we’ll leave it up to you to experience the actual endings.
You can Stop reading at this point if you don't want to have anything spoiled; otherwise, be forewarned: heavy spoilers ahead!