Alternate Costumes
All of the following are unlocked in konquest mode, usually found in a hidden chest.
Ashrah's Alternate Costume
Defeat the Ice Beast you encounter in Arctika and open the chest that appears.
Baraka's Alternate Costume
Kill all of the enemies in the final room of the Tekunin Warship and open the cheast that appears.
Cyrax's Alternate Costume
Kill all of the enemies in the third room of the Tekunin Warship and open the chest that appears.
Dairou's Alternate Costume
Open the chest at the end of the second ice hallway at the beginning of the Lin Kuei Temple Entrance.
Darrius' Alternate Costume
In a chest behind a discolored wall at the begining of the Lin Kuei Temple where you are attacked by Lin Kuei Archers.
Drahmin's Alternate Costume
In the Netherrealm after you defeat Drahmin, shoot down the bat creature over the nearby cliff and open the chest that appears.
Ermac's Alternate Costume
Found in a chest by the left wall in the room where you get attacked by the Red Commandos for the second time.
Frost's Alternate Costume
Break all of the tombs lining the wall in the room where you meet Frost.
Fujin's Alternate Costume
Defeat all of the Red Dragon Soldiers at the beginning of the Charred Mountain.
Hotaru's Alternate Costume
In a chest close to the wall in the second room of the Tekunin Warship.
Hsu Hao's Alternate Costume
In a chest on the right walkway after you wake up on the Tekunin Warship.
Jade's Alternate Costume
Defeat all of the Lin Kuei at the very beginning of the Lin Kuei Palace and open the chest that appears.
Jarek's Alternate Costume
Open the right chest in the room where you fight with the Ice Scepter.
Jax's Alternate Costume
Once you enter Arctika turn around and go to the left to find an invisable chest.
Johnny Cage's Alternate Costume
Costume Defeat the Tengu Guards at the beginning of Arctika and open the chest that appears.
Kai's Alternate Costume
In an invisable chest behind a breakable discolored wall to the right as you enter the third area of Lin Kuei Temple Entrance in Arctika.
Kano's Alternate Costume
In an invisable chest to the left as you enter the last room of the Temple of Argus.
Kenshi's Alternate Costume
Defeat all of the Tengu Ninjas with the given sword in Arctika.
Kira's Alternate Costume
Step on the second Giant Spider in Botan Jungle and open the chest that appears.
Kitana's Alternate Costume
Perform a Fatality on Wi Lae, leader of the Tengu Ninjas.
Kobra's Alternate Costume
In an invisable chest behind the first monoth in the Botan Jungle.
Kung Lao's Alternate Costume
Found in a chest to the right after you enter the Temple of Argus.
Mavado's Alternate Costume
Inside an invisible chest on the left part of the room where you do battle after you recieve the Supermove: Time Stop.
Motaro's Alternate Costume
After the third training obelisk, during the time you must gather crystals go to the left side of this area and open the chest there.
Nitara's Alternate Costume
After you defeat the Undead Revenants for the first time in the Netherrealm, jump down the left most cliff instead of the right. Open the nearby chest
Noob Saibot's Alternate Costume
Defeat all of the Shadow Ninjas the first time you encounter then in the
Lin Kuei Palace and open the chest that appears.
Quan Chi's Alternate Costume
Step on the rat in the tunnel after you travel through Door A1 in the Red
Dragon Caverns. Open the chest that appears
Rain's Alternate Costume
Open the chest at the end of the area in Arctika where you are attacked by Red Dragon Spies and before you meet Rain.
Reptile's Alternate Costume
Defeat the Hybrid Dragons you encounter in the Red Dragon Caverns and open the chest that
Sareena's Alternate Costume
Defeat Kai, Serenna, and Jatakka and open the chest that appears.
Shinnok's Alternate Costume
Once you get to the area in the Netherrealm with the falling rocks go to the leftmost side and open the chest that you find there.
Sindel's Alternate Costume
Complete the third training obelisk.
Smoke's Alternate Costume
Defeat Smoke and the chest with it inside with appear.
Sonya's Alternate Costume
In an invisable chest to the left of the gate in the area after you defeat Sonya.
Stryker's Alternate Costume
Break the wall on the right of the hallway after the Shadow Stalkers. Travel to the end of it and open the chest in the left aclove.
Sub-Zero's Alternate Costume
Open the chest to the right of the statue of your mother after your fight with Sub-Zero.
Thanks to gamefaqs for the list
All of the following are unlocked in konquest mode, usually found in a hidden chest.
Ashrah's Alternate Costume
Defeat the Ice Beast you encounter in Arctika and open the chest that appears.
Baraka's Alternate Costume
Kill all of the enemies in the final room of the Tekunin Warship and open the cheast that appears.
Cyrax's Alternate Costume
Kill all of the enemies in the third room of the Tekunin Warship and open the chest that appears.
Dairou's Alternate Costume
Open the chest at the end of the second ice hallway at the beginning of the Lin Kuei Temple Entrance.
Darrius' Alternate Costume
In a chest behind a discolored wall at the begining of the Lin Kuei Temple where you are attacked by Lin Kuei Archers.
Drahmin's Alternate Costume
In the Netherrealm after you defeat Drahmin, shoot down the bat creature over the nearby cliff and open the chest that appears.
Ermac's Alternate Costume
Found in a chest by the left wall in the room where you get attacked by the Red Commandos for the second time.
Frost's Alternate Costume
Break all of the tombs lining the wall in the room where you meet Frost.
Fujin's Alternate Costume
Defeat all of the Red Dragon Soldiers at the beginning of the Charred Mountain.
Hotaru's Alternate Costume
In a chest close to the wall in the second room of the Tekunin Warship.
Hsu Hao's Alternate Costume
In a chest on the right walkway after you wake up on the Tekunin Warship.
Jade's Alternate Costume
Defeat all of the Lin Kuei at the very beginning of the Lin Kuei Palace and open the chest that appears.
Jarek's Alternate Costume
Open the right chest in the room where you fight with the Ice Scepter.
Jax's Alternate Costume
Once you enter Arctika turn around and go to the left to find an invisable chest.
Johnny Cage's Alternate Costume
Costume Defeat the Tengu Guards at the beginning of Arctika and open the chest that appears.
Kai's Alternate Costume
In an invisable chest behind a breakable discolored wall to the right as you enter the third area of Lin Kuei Temple Entrance in Arctika.
Kano's Alternate Costume
In an invisable chest to the left as you enter the last room of the Temple of Argus.
Kenshi's Alternate Costume
Defeat all of the Tengu Ninjas with the given sword in Arctika.
Kira's Alternate Costume
Step on the second Giant Spider in Botan Jungle and open the chest that appears.
Kitana's Alternate Costume
Perform a Fatality on Wi Lae, leader of the Tengu Ninjas.
Kobra's Alternate Costume
In an invisable chest behind the first monoth in the Botan Jungle.
Kung Lao's Alternate Costume
Found in a chest to the right after you enter the Temple of Argus.
Mavado's Alternate Costume
Inside an invisible chest on the left part of the room where you do battle after you recieve the Supermove: Time Stop.
Motaro's Alternate Costume
After the third training obelisk, during the time you must gather crystals go to the left side of this area and open the chest there.
Nitara's Alternate Costume
After you defeat the Undead Revenants for the first time in the Netherrealm, jump down the left most cliff instead of the right. Open the nearby chest
Noob Saibot's Alternate Costume
Defeat all of the Shadow Ninjas the first time you encounter then in the
Lin Kuei Palace and open the chest that appears.
Quan Chi's Alternate Costume
Step on the rat in the tunnel after you travel through Door A1 in the Red
Dragon Caverns. Open the chest that appears
Rain's Alternate Costume
Open the chest at the end of the area in Arctika where you are attacked by Red Dragon Spies and before you meet Rain.
Reptile's Alternate Costume
Defeat the Hybrid Dragons you encounter in the Red Dragon Caverns and open the chest that
Sareena's Alternate Costume
Defeat Kai, Serenna, and Jatakka and open the chest that appears.
Shinnok's Alternate Costume
Once you get to the area in the Netherrealm with the falling rocks go to the leftmost side and open the chest that you find there.
Sindel's Alternate Costume
Complete the third training obelisk.
Smoke's Alternate Costume
Defeat Smoke and the chest with it inside with appear.
Sonya's Alternate Costume
In an invisable chest to the left of the gate in the area after you defeat Sonya.
Stryker's Alternate Costume
Break the wall on the right of the hallway after the Shadow Stalkers. Travel to the end of it and open the chest in the left aclove.
Sub-Zero's Alternate Costume
Open the chest to the right of the statue of your mother after your fight with Sub-Zero.
Thanks to gamefaqs for the list