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