Here is the full list of all 31 Kill Strain trophies - there are 14 bronze, 10 silver, 6 gold and 1 platinum.
Unlock All trophies
Kill 50 Mutants with a MEC
Turn your first Mercenary as a starting Mutant
Kill 100 Alpha Strain Pods by throwing an ARCC or with a MEC
Upgrade 3 Masteries to Max Tier
Deal 100,000 damage to Mutant base
Upgrade a Mastery to Max Tier
Equip a Mastery to a Mercenary and Mutant
Collect 20 unique Augments
Escape death by turning into a MEC with less than 5% health
Deal 100,000 damage to a Mercenary base
Reach lifetime score of 666,666 points
Open an Augment pack
Complete 10 Missions
Kill a total of 80 Mercenaries and 40 Mutants
Turn 20 Mercenaries
Be the last Mercenary on your team by the end of a match
Complete 30 matches of Kill Strain
Save a teammate Mercenary from turning
Survive a Mutant drag by struggling
Complete matches starting as 5 different characters (Mercenaries or Mutant)
Kill 10 Mutants
Activate 20 MECs
Spread Strain 250 times
Get 8 kills without dying in a match
Get turned and then turn an ex Mercenary teammate in a match
Complete a game as a Mercenary and starting Mutant
Get at least 3 Gold medals in a match
Take 10,000 player damage as a Mutant in one life
Kill 10 Mercenaries
Deliver an ARCC at the Drop Zone and kill an Alpha Strain Pod in one match