Here is the full list of all 50 Injustice: Gods Among Us achievements worth 1,000 gamerscore.
Defeat every Villain With Batman
Win with Batman using every special move and his Supermove
Win a match with Green Arrow using only arrows
Knock opponent through all transitions across all levels
Send an opponent through all three Metropolis transitions in one fight
Make a comeback when at low health (10% or less)
Perform 8 throws and win in a multiplayer match
Win a match as Deathstroke without missing a shot (minimum 12 shots)
Knock an opponent through a transition
Use every interactable and win in a multiplayer match
Enter Online Practice with someone on your friends list
Win a multiplayer match with a timeout
Vote Correctly in a KOTH match
Complete Tutorial
Win a single online match
Enter Practice Mode
Unlock a costume in the Archives
Complete Classic Battle with any character
Reach Level 10
Equip a new Background Image
Equip a new Icon
Equip a new Character Portrait
Complete 1 S.T.A.R. Lab Mission
Get 3 stars on 1 S.T.A.R. Lab Mission
Win a match with the super move of any character
View Your Hero Card
Win a Clash sequence with any character
Complete Classic Battle with all characters
Complete Battle Mode
Beat All S.T.A.R. Lab Missions (Excluding DLC)
Win all story mode minigames
Reach Level 100
Complete 50% of Story Mode
Complete 100% of Story Mode
Dethrone the King in an online match
Defeat a Survivor
Win 100 complete Online Matches
Play 200 complete Online Matches
Win 1 complete Ranked match
Win 10 complete Ranked matches
Get 100 Stars in S.T.A.R. Lab Mode
Complete All S.T.A.R. Lab Missions with 3 Stars
Perform a 10 hit combo with every character
Perform every character's supermove
Perform every special move of every character
Perform every Meter Burn special move of every character
Perform every level interaction once
Unlock all costumes in the Archives
Unlock everything in Archives
Cause maximum damage in all Arenas (does not include Practice mode)