I think the ??? is the House of the Dead 3 Extreme Mode.
From GameFAQs..
House of the Dead 3 Extreme Mode
In order to unlock the one-player only extreme mode for House of the Dead 3, you need to beat both House of the Dead 2 and House of the Dead 3. Extreme mode requires you to hit weak points to kill enemies and allows the use of a blocking attack.
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