Desktops 1:
To unlock Desktops 1, beat all seven Metal slug games on Normal difficulty with limited continues.
Desktops 2 and Special Music:
To unlock Desktops 2 and Special Music, beat all seven Metal Slug games on Hard difficulty with limited continues.
Art galleries:
Unlock the following Art Galleries by beating the corresponding games:
ART GALLERY – GAME
Art Gallery 1 – Metal Slug
Art Gallery 2 – Metal Slug 2
Art Gallery 3 – Metal Slug X
Art Gallery 4 – Metal Slug 3
Art Gallery 5 – Metal Slug 4
Art Gallery 6 – Metal Slug 5
Art Gallery 7 – Metal Slug 6
Tonko Gallery – Beat all seven Metal Slug games with limited continues.
Easy Tokens:
To get easy tokens, after you defeat the Final Boss on Metal Slug 3 or Metal Slug 5, save the game and quit to the main menu once the credits start. You will get five tokens. Reload the game and quit to get five more tokens. Repeat as desired.