there are six Premier skins in "Injustice: Gods Among Us" that player can unlock by connecting his PC/Console version of the game with Mobile version[injustice-mobile.fandom.com] (available for Android or iOS devices)

six skins are available in total, and player unlocks them in the following ways:

• Batman Beyond - obtain a Batman card in Injustice Mobile

• Harley Quinn Arkham City - obtain a Joker card in Injustice Mobile

• Green Lantern New 52 - complete a Bonus Battle in Injustice Mobile

• The Flash New 52 - complete a Challenge Mode Ladder in Injustice Mobile

• Superman Lockdown - complete all Battles in Injustice Mobile

• Bane Knightfall - rate Injustice Mobile in a store

if you don't want to waste your time on Injustice Mobile, or that app is not available in your country, or it is year 202X and app is no longer available - then you can easily unlock all those skins in a PC version with a small text file

• download that archive
  

  https://drive.google.com/file/d/1iwY7J_has7_RLxzf1zxcCb1Dq6cEWutk/view

• inside the archive there will be a "UnlockCostumes" folder. place it into the folder
  

  ...\STEAM\steamapps\common\InjusticeGodsAmongUs_UltimateEdition\DiscContentPCG\DLC\

• launch the game and check out the skins in the game (either in Archive, or in Battle). if you see new skins, then you done everything right. enjoy!

if you want to thank me...

...then check my guide about fixing various game issues: launching, crashing, optimization, stuttering, gamepads, etc. the guide is huge, but the topic is broad to begin with
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1935376439