CASSIE CAGE:

Endurance - Beat the Klassic Tower with Cassie Cage or (0, 10) in the Krypt (Dead Woods Cemetery)

D'VORAH:

Kytinn Queen - Beat the Klassic Tower with D'Vorah or (-7, 12) in the Krypt (Spider Cave)

ERMAC:

Tournament - Beat the Klassic Tower with Ermac or (-21, 9) in the Krypt (Dead Woods Cemetery)

Pharaoh - Horror Pack DLC

ERRON BLACK:

Outcast - Beat the Klassic Tower with Erron Black or (-2, 9) in the Krypt (Dead Woods Cemetery)

FERRA/TORR:

Master and Servant - Beat the Klassic Tower with Ferra/Torr or (6, 8) in the Krypt (Spider Cave)

JACQUI BRIGGS:

Boot Camp - Beat the Klassic Tower with Jacqui Briggs or (-8 8) in the Krypt (Dead Woods Cemetery)

JAX:

Tournament - Beat the Klassic Tower with Jax or (-19, 7) in the Krypt (Dead Woods Cemetery)

Revenant - Win 15 matches via Double Flawless victory

Farmer - Complete the 3rd Bracket in Ladder Mode on MKX Mobile

Carl Weathers - Predator/Prey DLC Pack

MK3 - Klassic DLC Pack 2

JOHNNY CAGE:

Tournament - Beat the Klassic Tower with Johnny Cage or (1, 6) in the Krypt (Shao Kahn's Temple)

Hotshot - Go on a 10 win streak in public Survivor KoTH

Ninja Mime - Log into WBPlay on MKX Mobile and Console/PC

Soccer - Brazil DLC Pack

Commando - Predator/Prey DLC Pack

KANO:

Tournament - Beat the Klassic Tower with Kano or (-15, 19) in the Krypt (Dead Woods Cemetery)

Revolution - Kold War DLC Pack

MK1 - Klassic DLC Pack 1

KENSHI:

Tournament - Beat the Klassic Tower with Kenshi or (6, 17) in the Krypt (Shao Kahn's Temple)

Ronin - Samurai DLC Pack

KITANA:

Tournament - Beat the Klassic Tower with Kitana or (1, 6) in the Krypt (Dead Woods Cemetery)

Revenant - Give 260 respect in KoTH

Dark Empress - Random Living Tower drop

Jingu - Samurai DLC Pack

Klassic - Level up a character to 40 in MKX Mobile

KOTAL KAHN:

Osh-Tekk Warrior - Beat the Klassic Tower with Kotal Kahn or (-8, 8) in the Krypt (Shao Kahn's Temple)

KUNG JIN:

Shadow - Beat the Klassic Tower with Kung Jin or (-1, 4) in the Krypt (Gallery of Shadows)

Kung Lao:

Tournament - Beat the Klassic Tower with Kung Lao or (-3, 19) in the Krypt (Dead Woods Cemetery)

Revenant - Win 26 public KoTH matches

Gaucho - Brazil DLC Pack

MK3 - Klassic DLC Pack 2

LIU KANG:

Tournament - Beat the Klassic Tower with Liu Kang or (1, 11) in the Krypt (Shao Kahn's Temple)

Revenant - Win 26 online ranked matches

Dark Emperor - Beat 10 Challenge Towers

Capoeira - Brazil DLC Pack

MK1 - Klassic DLC Pack 1

MILEENA:

Tournament - Beat the Klassic Tower with Mileena or (-18, 9) in the Krypt (Dead Woods Cemetery)

Kahnum - Get gold on the Endless Kombat Tower

Klassic - Finish a Challenge Ladder on MKX Mobile

Vampiress - Horror DLC Pack

QUAN CHI:

Tournament - Beat the Klassic Tower with Quan Chi or (-1, 8) in the Krypt (Dead Woods Cemetery)

MK4 - Klassic DLC Pack 2

RAIDEN:

Tournament - Beat the Klassic Tower with Raiden or(-17, 19) in the Krypt (Dead Woods Cemetery)

Dark - (0, 14) in the Krypt (Shao Kahn's Temple)

Future - Log into WBPlay

REPTILE:

Tournament - Beat the Klassic Tower with Reptile or (15, 16) in the Krypt (Spider Cave)

Kraken - Horror DLC Pack

SCORPION:
Tournament - Beat the Klassic Tower with Scorpion or (5, 28) in the Krypt (Spider Cave)

Hanzo Hasashi - Beat Scorpion's Chapter in Story Mode

Injustice - Play 100 Multiplayer matches in MKX Mobile

Gold - Kollector's Edition Exclusive

Kold War - Free DLC

Infrared - Predator/Prey DLC Pack

SHINNOK:

Wrathful - Beat the Klassic Tower as Shinnok or (0, 17) in the Krypt (Dead Woods Cemetery)

Samurai - Samurai DLC Pack

SONYA BLADE

Tournament - Beat the Klassic Tower as Sonya Blade or (-7, 25) in the Krypt (Shao Kahn's Temple)

Major Blade - Beat Sonya Blade's Chapter in Story Mode

Motherland - Kold War DLC Pack

MK1 - Klassic DLC Pack 1

Sub-Zero:

Kuai Lang - Beat the Klassic Tower as Sub-Zero or (3, 3) in the Krypt (Lost Mausoleum)

Revenant - Beat 10 Test Your Might stages

Blue Steel - DLC

Tundra - Kold War DLC Pack

https://www.reddit.com/r/MortalKombat/comments/3f7wa0/list_of_how_to_unlock_all_alternate_costumes/

got all my info from here!!!