NOTE: As their name suggests hints are not exactly Mortal Kombat: Armageddon cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing Mortal Kombat: Armageddon even more entertaining.

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.
Bo’Rai Cho’s Alternate Costume: Open the chest that appears after you defeat the Wraiths of Shinnok’s Spire.
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.
Goro’s Alternate Costume: In an invisible chest to on the left side of the first area in Shao Khan’s Fortress and directly to the right of a musical note.
Havik’s Alternate Costume: Defeat all of the demons in the second area of Shinnok’s Spire.
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.
Li Mei’s Alternate Costume: In the second area of Shinnok’s Spire walk around the edge of the room until you find an invisible chest.
Liu Kang’s Alternate Costume: As you enter Shao Kahn’s Fortress, turn around and run foward to find an invisible chest.
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.
Mileena’s Alternate Costume: After you defeat Mileena hit the Ground Pound Switch in front of you and open the chest that appears.
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.
NightWolf’s Alternate Costume: After you defeat the Giant Skulls in Edenia, travel up the path until all of the chests appear. The first one on the right has this in it.
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.
Raiden’s Alternate Costume: When or after fighting the Shao Khan Collosus go into the first room on the left
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.
Reiko’s Alternate Costume: In a chest in Shao Khan’s Fortress, as you enter the first area with blades travel down a hall to the left.
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.
Shang Tsung’s Alternate Costume: At the beginning of Shao Khan’s Fortress, hit the ground pound icon which is located to the right and up the ramp.
Shao Kahn’s Alternate Costume: Open the chest that appears after you defeat Shao Khan’s Statue.
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.
Shujinko’s Alternate Costume: Hit the ground pound icon in one of the cells after you defeat The Executioner in Shao Khan’s Dungeon.
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.
Tanya’s Alternate Costume: Found in Shao Khan’s Dungeon, after you make it to the cell area. You must hit the ground pound icon and then go back to the third cell on the right.
Taven’s Alternate Costume: After you defeat the Giant Skulls in Edenia, travel up the path until all of the chests appear. The third one on the left has this in it.

Hidden Characters
By accomplishing certain tasks in Konquest mode, new characters can be unlocked.

Blaze: Obtain 50 relics in Konquest
Daegon: Obtain 30 relics in Konquest
Meat: Obtain 10 relics in Konquest
Taven: Finish the storyline in Konquest

Originally from ActionTrip