Here's what I was using when I caught that Mewtwo:
Code:
[Force Shiny]
040A0000 0069B780 1400000E
040A0000 0069B7D0 D503201F
040A0000 0069B80C D503201F
040A0000 0069B820 14000031
[6IV On]
040A0000 00CFC324 528003E1
040A0000 00CFC330 528003E1
040A0000 00CFC33C 528003E1
040A0000 00CFC348 528003E1
040A0000 00CFC354 528003E1
040A0000 00CFC360 528003E1
[Always Encounter Pokemon]
040A0000 02FC7FC4 18000161
040A0000 02FC7FC8 34000041
040A0000 02FC7FCC 790067E1
040A0000 02FC7FD0 18000121
040A0000 02FC7FD4 79006BE1
040A0000 02FC7FD8 18000101
040A0000 02FC7FDC 79006FE1
040A0000 02FC7FE0 180000E1
040A0000 02FC7FE4 390103E1
040A0000 02FC7FE8 F9403A60
040A0000 02FC7FEC 1774D09A
040A0000 02FC7FF0 00000000
040A0000 02FC7FF4 00000000
040A0000 02FC7FF8 00000000
040A0000 02FC7FFC 0000000A
040A0000 00CFC250 148B2F5D
[Always Level 1]
040A0000 00CFC498 52800022
[Encounter 150 Mewtwo]
040A0000 02FC7FF0 00000096
[Encounter Item Masterball]
040A0000 02FC7FF8 00000001
I toggled all of those on standing inside Hotel Z, then ran outside into Area 1, where all spawned Pokemon were shiny Mewtwo (the first Pokemon I caught happened to be an Alpha, I wasn't using a code for Alphas).
Once you are done catching Pokemon, you should disable all the codes in use and then toggle the Restore Code on.
Code:
[Restore Code]
040A0000 00859534 3903C288
040A0000 027C6100 B9004008
040A0000 027C6128 B9004008
040A0000 007AAC98 F9000102
040A0000 00D1A344 1A9F27E0
040A0000 0069B780 540001C1
040A0000 0069B7D0 540001A1
040A0000 0069B80C 540003A0
040A0000 0069B820 54000621
040A0000 00152794 A9405514
040A0000 00CFC324 394143E1
040A0000 00CFC330 39414BE1
040A0000 00CFC33C 394153E1
040A0000 00CFC348 39415BE1
040A0000 00CFC354 394163E1
040A0000 00CFC360 39416BE1
040A0000 00CFC2B0 79408BE1
040A0000 00CFC2BC 79408FE1
040A0000 002E7798 BD01AA61
040A0000 00CFC498 394103E2
040A0000 00BFE310 4E21C400
040A0000 00CFC250 F9403A60
040A0000 004491C4 12001C08
040A0000 00BB301C 0B160108
040A0000 02BD7E74 B50000A0