Score display(House Of The Dead 2):
To unlock Score display in House of the Dead 2, go the title screen and press Left two times, Right three times, Left, Right, A.
Completion bonuses(House Of The Dead 2):
To unlock Very Easy difficulty, Very Hard difficulty, and the ability
to increase lives to five and continues to nine, beat the game.
To unlock the House Of The Dead 2 mini-game, beat the game in Original
mode. It will become unlocked when you select House Of The Dead 2 at
the main menu.
Completion bonuses(House Of The Dead 3)
To unlock Very Easy difficulty, Very Hard difficulty, and the ability
to increase lives to five and continues to nine, beat the game.
Extreme mode(House Of The Dead 3):
To unlock Extreme mode in House Of The Dead 3, beat House Of The Dead 2 and House Of The Dead 3.
Free Play mode(House Of The Dead 3):
To unlock Free Play mode which gives you infinite credits, beat the
first two chapter of House Of The Dead 3 on Extreme difficulty.