If Marshadow wins
(1)Hoopa 8+10
(3)Victini 8+8
(2)Marshadow 8+6
(1)Diancie 7+6
(3)Raikou 6+6
(4)Shaymin 6-4
(4)Regi
(2)Melo
We need 2 of:
-Regi win/tie or our loss + shaymins win is below 14 (if equal we tie Shaymin)
-Our loss - Melo's win is below is below 4 (if equal we tie Marshadow)
-Victini win/tie
-Our loss - Raikous win is below 2 (if equal we tie Victini)

Case by case:

We lose 0-12
We need 2 of:
-Regi win/tie or Shaymin 7-5 win (tie with them)
-Victini win/tie
-Raikou 11-1 win (we tie with Victini) or better
-Melo win 10-2 (we tie with Marshadow) or better

We lose 1-11
We need 2 of:
-Regi win/tie or Shaymin 8-4 win (tie with them) or worse
-Victini win/tie
-Raikou 10-2 win (we tie with Victini) or better
-Melo win 9-3 (we tie with Marshadow) or better

We lose 2-10
We need 2 of:
-Regi win/tie or Shaymin 9-3 win (tie with them) or worse
-Victini win/tie
-Raikou 9-3 win (we tie with Victini) or better
-Melo win 8-4 (we tie with Marshadow) or better

We lose 3-9
We need 2 of:
-Regi win/tie or Shaymin 10-2 win (tie with them) or worse
-Victini win/tie
-Raikou 8-4 win (we tie with Victini) or better
-Melo win 7-5 (we tie with Marshadow) or better

We lose 4-8
We need 2 of:
-Regi win/tie or Shaymin 11-1 win (tie with them) or worse
-Victini win/tie
-Raikou 7-5 win (we tie with Victini) or better
-Melo win

5-7
We need 1 of:
-Regi win/tie or Shaymin 12-0 win (tie with them) or worse
-Melo win