To play as Onslaught, beat Onslaught in the Arcade Battle mode. You'll be able to access him right under Wolverine.

Finish the game with Venom then press up at Chun Li.

Finish the game with Hulk then press up at Ryu.

Finish the game with Megaman/Rockman then press right at Megaman/Rockman.

Finish the game with War Machine then press up at Zangief.

First select Spider-Man or Venom as your character. Then while at the match execute a web throw and throw your opponent at the right side 2 times. At the second time the wall will break up. There you will find E.Honda's old stage.

To play as Evil Ryu you must hold on start and press L1 and R1 and you can play as Evil Ryu at any mode.

Finish the game with Morrigan then press down at War Machine.

Finish the game with Chun Li then press down at Gambit.

Highlight Zangief at the character selection screen. Hold select and press any action button. You should now be using Dark Zangief.

Go to the main menu then highlight the options menu and press and hold (select) then press (start) This option will allow you to max the level of your ex bar and many more.

Select Ryu as your character. After reaching level 1 perform his hurricane kick(half moon)but instead of pressing a kick press the following buttons:
*Hard Punch - Change to Akuma
*Medium Punch - Change to Ken
*Low Punch - Change to Ryu

To get the hidden charecters you have to beat the game with certain people beat it with certain people

anyone = Onslaught
Chun-Li = Shadow Lady
Hulk = Orange Hulk
Megaman = Roll
Morrigan = her other half
War Machine = Gold War Machine
Venom = Red Venom

They are in hidden spaces under,next to, and over other people