Instructions
Complete the loyalty missions for every member of your squad before starting the final mission. If a squad mate is not loyal to Shepard, the likelihood of them being killed is raised considerably.
Purchase the ship upgrades offered by Tali, Jacob and Garrus. This upgrades will be available once you have completed each of their respective loyalty missions. Without these upgrades, random members of your team will be killed when approaching the Collector's base in the final mission.
Assign Tali, Legion or Kasumi to hack the vents when first assaulting the Collector base. Any other teammate will fail and die at this task.
Choose Garrus, Jacob or Miranda as the 1st fire squad leader. If another squad mate is chosen, a random squad mate will be killed in the firefight.
Assign Samara or Jack with upgraded implants to hold the kinect barrier. Any other squad mate will not be able to maintain the shield and a random squad member will be eaten by bugs.
Select Jacob, Garrus or Miranda to lead the 2nd fire squad. A wrong choice will not be able to hold the line and team member will be killed.
Send Mordin back as the escort with the rescued crew members. Mordin is the most likely to be killed when holding the line with the 2nd fire squad, so choosing to send him back as the escort eliminates that possibility.
Take Jack, Tali, Kasumi, Thane, Miranda or Samara to confront the harbinger and the baby reaper. You can select two of the listed teammates to take into battle.