To get Psylocke use arcade mode and finish
the game using Wolverine.


To get Spiderman use arcade mode and fight 
till you face and defeat Spiderman. Now 
highlight Cyclops and Hold L1 at the Character
select screen.


To get Professor Xavier successfully complete
the game as Juggernaut (then, highlight 
Magneto and hold L1 at the character selection
screen).


To get Juggernaut successfully complete the 
game using all default characters and Psylocke
in arcade mode.