Select anyone and keep losing, just don't pause and retry. Instead, select "Retry" when you lose. The difficulty will drop and you will start regenerating health between fights. Once you lose ten to fifteen fights, the AI pretty much just stands still.
On "The Living Forest" stage in Arcade mode, repeatedly press DOWN + BACK when you see Smoke pop out from behind one of the trees to have classic Smoke challenge you. This will earn you the "Hide And Seek" achievement or trophy. Note: Win 2,000 coins for defeating him.
When Noob Saibot is standing in the background during a fight in the "Temple" (Cathedral) stage in Arcade mode, win all rounds without blocking. Classic Noob Saibot will challenge you and you'll get 1,000 coins for defeating him. Note: To get classic Noob Saibot to appear, return to the player selection screen and begin the match again. Repeat until he appears.
Clearing story mode earns you a decent amount of koins for buying unlockable fatalities, costumes, etc. in the Kombat Krypt. If you grow tired of this, you can use Arcade Mode to farm for koins.
Set the game difficulty to ''Very Easy'' and three rounds. Try getting a Flawless Victory (earns 1000 koins) each round. Perform a fatality for an extra 250 koins. This is a tedious but reliable method to earn a potential 3250 koins for a couple minutes of work.
In the Krypt, return through the Meadow of Despair toward the Nekropolis until you cannot walk anymore. Go slightly to the right so that the stairs going up to the Nekropolis are about half on the screen. Then, go to the map that shows you all of the Krypt areas and your marker will show where you are standing. Hold B to exit and return to the Krypt to see "SEC 4" on the screen. Purchase it and a chest will appear from the ground containing 5,000 Koins. Note: You might have to try a few times to get the positioning correct.
About half way down the wall, next to the Hollow of Infestation, access the Krypt map by pressing Y. Then, exit the map by holding B. When you see "SEC2" appear at the bottom of your screen, press A to purchase it and receive 5,000 Koins.
Watch a King Of The Hill match as a spectator in Theater mode, then highlight your avatar and press the X to display the "Avatar Move" menu. Afterward, activate the following moves by performing the corresponding combos:
Usually you can't use a Babality on Goro or Kintaro. To do so, play on Normal or harder and perform a Babality on Shang Tsung and NEVER LOSE A ROUND. This will result in an automatic Babality on these bosses. If you use Bablities on both of these bosses, you'll use it on Shao Khan.
On "The Pit 2" (Night) stage in Arcade mode, get a double flawless victory and perform a stage fatality after a shadowy figure flies across the moon to have classic Reptile challenge you. This will also earn you the "Pit Master" achievement. Note: Win 5,000 coins for defeating him.
In floor 37 of the Challenge Tower you must fight Kano as Kabal. Attack him to get as many koins as you want, but make sure you press start and hit retry before you die or lose too much life. You'll notice that your koins haven't reset.
Alternatively, on floor 127 of the Challenge Tower, you will fight Director as Johny Cage and can pull off the same exploit here.
To easily defeat Shao Kahn in the final battle, retreat as you would normally. He will then do one of three actions; throw the spear, throw the hammer, or laugh/taunt. When he throws the hammer or taunts, teleport behind him and quickly uppercut him, then retreat again. When he throws the spear, teleport at the first possible instant and uppercut. If you are too slow, he will turn and attack. The best way to attack when he throws the spear is to teleport and jump over his head to dodge his attack, then deliver a drop kick followed immediately by the Electric Fly. Always retreat after each hit. Also, duck to dodge the spear instead of blocking, which will save you from losing health.
When fighting Shao Kahn in the normal ladder, defeat him easily by simply backing up continually. When he taunts or throws his spear, he is open for projectile attacks. Teleports are also useful. Be sure to retreat after each hit you land.
Reach Stage 61 where Cyrax has 30 seconds to drop bombs in a moving bucket. Then, pause and hit RETRY before the timer runs out. You get 50 Koins for each bucket and accumulates Koins until you let the timer expire. It's takes a while but works.
Perform a Babality on a boss character by executing the following tasks:
Play at Medium difficulty or higher and win every match (individual rounds are just fine, but no continuing).
Do not use the block button at all in the final round of the fight with Goro/Kintaro. Babality will automatically activate as soon as you win the match.
Play at Medium difficulty or higher and do not lose a match. (individual rounds are just fine, but no continuing). Perform a Babality on EVERY character along the ladder, including Shang Tsung and Goro/Kintaro. Do not use the block button at all during the final round of the fight with Shao Khan. Babality will automatically activate upon winning the match.
Note: Classic Noob and Smoke DLC are required. Press START on Noob to open the costume select menu. Then go to MK2 and press START. Use Noob's moves where he uses his clone; you will see Smoke instead of the clone.
When fighting Shang Tsung in Arcade mode, get a double flawless victory and perform a fatality to have classic Jade challenge you in Goro's Lair. This will earn you the "You Found Me!" achievement. Note: Win 5,000 coins for defeating her.
When you knock an opponent down and uppercut them at the right time, Dan Forden will appear in the bottom right hand corner and say "Toasty!" in a very high-pitched manner. Dan Forden is wearing a blue-gray shirt with a piece of toast super-imposed on it. This is an old Mortal Kombat joke that started during on Mortal Kombat 2.
Press 'Start while selecting a stage in Versus mode. Shao Kahn laugh, indicating that the stage's music will be replaced with a song from a previous Mortal Kombat title. Note: The following stages have no alternate soundtrack:
Desert, The Flesh Pits Hell, Rooftop (Dusk) Shao Kahn's Throne Room Shang Tsung's Gardens Shang Tsung's Gardens (Night) The Bell Tower. The Courtyard (Night)