XX Mission

XX Mission
Developer: UPL Publishers: UPL (JP), United Artists Theatre Amusements (US) Platform: Arcade (custom) Released in JP: September 1986 Released in US: August 1987 This game has hidden developer credits. This game has unused graphics.

XX Mission is a standard shoot 'em up with no stand-out features. It might have been more interesting with an additional X.

Hidden Credits

There's a set of credits (and a build date) hidden in the game that can be accessed by entering and activating the following code in MAME's xxmissio.xml cheat file.

  <cheat desc="Game Credits">
    <script state="on">
      <action>maincpu.pb@E146=01</action>
    </script>
    <script state="off">
      <action>maincpu.pb@E146=00</action>
    </script>
  </cheat>

Not content with having just one set of hidden credits, another is stored in the sub-CPU starting at 0x00FC:

 Music,effect and Produce By T.fujisawa 
 Software By S.Satoh 
 Desing By A.tsunoda and T.fujisawa 
 1986 UPL Limited !

Since you can never credit Tsutomu Fuzisawa enough, there's an additional credit in the object graphics bank.

(XX Source: Original TCRF research)