This is the final achievement that I got. I have a life, as do many of you, so I'm sure most of you won't be getting this the "legit" way. I know that with enough poking around you can find out how to get this quicker, but to make it easy for all of you, it is all gathered for you here in this one thread. So far using these methods, I mastered 1 character in about 1 hour or less (not including the time duration requirement one)
What you need to master each character:
-10000 pints of blood spilled
-24 hours game time played with character
I put these two together since u can't get the fatalities one without the victories. Go into versus mode (you need 2 controllers) and at the versus screen, using the 1, 2, and 4 buttons, put in the kombat kode:
0 4 4 | 4 4 0
It will look like 4 question marks (?) in the middle. This makes it so that it only takes one hit to finish the round. Also go to settings and set the rounds to 1. Then choose rematch and repeat. To save even more time, choose Sindel as your opponent and do a Babality on her. It is extremely quick and you get the "----- wins" almost immediately.
For this one, set the rounds in settings to 3, and go to versus mode TAG MATCH. Using two controllers, put in the following kombat kode:
4 6 6 | 4 6 6
It will look like ?, skull, skull, ?, skull, skull. This makes your super meter unlimited, so you can just keep doing xrays. Depending on which character you are using and how much damage their xray does, you can get 18-24 xrays per match.
10000 pints of blood spilled
This one is the easiest. Same as above, but instead of xrays, just do heaps of combos. Even if you are no good with the character, go into their move lists and just choose any one of their 3 hit combos, and keep doing it. Remember, set the rounds to 3 and do a TAG match to minimize the time to complete this one.
24 hours game time with character
This one is the one most people (including myself) are most angry about. Most of you have probably already heard about the exploit for this, but I'll say it anyway for those who don't. Go into TAG TEAM TRAINING MODE, and select the two characters you want the time to go on, and just leave your console on. You can leave it overnight too. The time will count for both people.
-ALWAYS use player 1's controller for the characters you want to master, and make sure you are signed into your profile on that controller. It will not count if you do it on a different controller/profile.
-After doing x hours in training mode toward the time duration requirement, DO NOT just turn off the xbox. Exit out of training mode, and go to nekropolis and check the stats, or else IT WILL NOT SAVE. Mortal kombat autosaves in between loading screens, and if you don't save, all your time will be wasted. I learned this the hard way..
-Install your game to your hard drive, or else your console will make loud noises, and it could damage it if left for long periods of times. (Xbox 360 only)
-You need a plug&play controller, or a play&charge cable for your controller. If you are using wireless, you cannot do the above exploit since the controller will turn itself off after a while, and will pause the game.
Hope this helps someone.