Whith this mod the allies are invulnerable from every damage for a diferent game experience.
The levels are from "The pillar of Autumn" to "the Library" included.
In the rest of the levels there aren't allies.

Exceptions:
-Hit in the back caused only by the player.
-Destruction of the vehicle that they are driving which can be destroyed, like, the ghost.

Additional data:

-The game kills some marines in certain momments of the campaign.
-In some maps in that the marines don't follow you, can happen that they become
 statues.

Obligatory spoilers(pretending to give the less references as possible):

-Along the campaign you can find a enemy marine that is also invulnerable, but,
 even in legendary can be avoid.
-Some type of enemy ataches to the marines and they can't be removed from them.