The key is as follows:

B = Beast   W = Wolverine  M = Magneto     X = Xavier
G = Gambit  C = Cyclops    A = Apocalypse  P = Psylocke

Tusk Stage     Brood Stage (Level 2)     Apocalypse Stage
A B P C        B P A C                   G W G W 
C M M P        A M M G                   C G M A

Omega Red      Juggernaut                Final Stage: 
X C X C        P B B G                   G W X C 
A C P X        W B P C                   C C P B