Requirements to become Mastery of a Fighter include:
100 Wins
150 X-Ray
100 ~alities (Any form of finishing move)
Spilled 10,000 pints of blood
24 hours play time with that char
For "My Kung Fu is strong" you have to do this for one fighter. For "My Kung Fu is stronger" you have to do it for all 27 characters (excluding DLC characters).
First you should work on X-Rays in 2 player tag team (requires 2 controllers). ClaytThaGreat said you should play matches with 3 rounds. That might be faster to get X-Rays done but you should play matches with 1 round to get also more fatalities.
(Example: You play 22 matches with 1 round each. If you can do 7 X-Rays in one match you will get 154 X-Rays and 22 Fatalities. If you set rounds to 3 you would get 192 X-Rays but only (!) 8 fatalities [8 matches with 3 rounds each].)
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Settings should be
Rounds: 1
Timer: Off
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At the loading screen input the following kombat kode 466-466 for unlimited super meter (-> X-Rays).
When you are done with X-Rays use the following kombat kode 044-440 for sans power (-> Fatalities). This way you can finish your oppenent with 1 punsh.
Use uppercuts for your blood spilled progress. Do not use Babalities because you spill more blood with Fatalities. I prefer to play on "Subway". The stage fatality is short (-> saves some time) and you spill a lot of blood.
Check stage fatality here:
Try to combine stuff. Example: If you have 85 wins and you only have 8500 pints do not enter any codes. Do not use uppercuts now. You will spill more blood if you spam "X". You can still work on fatalities but you also get some more blood spilled.
and now...how to save some time when you go for "My Kung Fu Is Stronger". There are 27 characters and you have to play/idle 24 hours with every character. You can get 26 characters done in tag team practice. Choose 2 characters and leave your PC on.
Problem: You have to waste 24 hours for the last character.
Solution: When you are done with 24 characters you have 3 characters left (character A, B and C).
Start boosting with character A and B and stop after ~12 hours. Now start boosting with character A and C. After 24 hours you are done with character A. So you can play with B and C for 12 more hours. This way you can always boost 2 characters at the same time.
Usually the achievement does not pop in tag team practice. Switch to any mode (ladder, online, 2 player versus) and play one match. Just finish the match and the achievement will pop.
Additional Infos: You can check your progress in the Nekropolis (Extras-> Nekropolis) for every character.utes.