If you have completed the main story, you can get this trophy by playing a War Zone mission with 3 of the AI Companions and not getting hit. The AI taking damage does not count as a player.
I did this on Stark Industries on Challenge 1 using hulk, Just spamming ranged rocks into the compound until the AI took out the elimination targets. One of my AI Companions went down and needed to be revived and the trophy still popped
Takes about 3 minutes.