When 'House of the Dead 2' Original mode has been completed the 'House of the Dead 2' mini-game will become available when you select 'House Of The Dead 2' again at the 'Main' menu. The mini-game has bonuses that are items from 'House Of The Dead 2's Original mode. You can't play the mini-game again until 'House Of The Dead 2's Original mode has once again been completed.
When you have beaten House of the Dead 2 and House of the Dead 3 Extreme mode for 1-Player will become an available option. In Extreme mode you have to hit the enemies weak points to kill them and you are able to use blocking attacks.