Secret Game - Super Xevious
Go to Xevious, then choose "Settings"->"Hardcore Options" and hit Xevious Version. Choose "Super Xevious", and press "Confirm". You will now be able to choose Super Xevious from the arcade and Score Attack menus. Super Xevious is a more difficult version of Xevious that was originally given a limited release.
Dig-Dug 2 Old Version
Go to the Arcade Menu then go to Dig-Dug 2. Go to the menu by touching the screen or by pressing [L]+[Start]. Go to Settings, then to Hardcore options, select "New Version" and switch it to Old. Now when you go to the Arcade Menu you can choose Dig-Dug 2 Old version.