Akuma:
     First go to SPIRAL for three seconds, then without stopping go in
this order:
SILVER SAMUARI, PSYLOCKE, COLOSSUS, ICEMAN, COLOSSUS, CYCLOPS, 
WOLVERNIE, OMEGA RED, SILVER SAMUARI
     Now  while  on  SILVER  SAMUARI wait for three seconds then press
short kick, fierce punch and roundhouse.

Get the Bosses (PC Only):
     This  code  will  let  you  use Magneto and Juggernaut. To do it,
simply  go  to  the  Option  menu by pressing f10 and then go into the
configuration  menu.  Once there, type in the word SPAM . After typing
in  the code, go into system and you will see a new option called BOSS
SELECT. Enable this option and then save the new settings. When saved,
start  a  normal  game  and  select a fighter and block mode. Now just
before  the  battle  loads hold all three punches down (if you want to
use Juggernaut) OR hold all 3 kicks down (if you want to use Magneto.)
Continue  to  hold  down  the  3  punches  or 3 kicks until the battle
finishes  loading.  You  should  now  be  able  to  use  your new boss
character.