To unlock debug mode, first, you have to unlock the classic NES version. Next, go to the main menu and enter the following command:
bombs_missle screw_atack
To get Image Gallery #1, scan 50% of the Creature and research data
To get Art Gallery 2, scan 100% of everything
To get Image Gallery #3, get 100% of items
To get Image Gallery #4, complete the game on Hard mode