Desktops 1 - Successfully complete all seven Metal Slug games on the Normal difficulty setting with limited continues to unlock the Desktops 1.

Desktops 2 and Special Music - Successfully complete all seven Metal Slug games on the Hard difficulty setting with limited continues to unlock the Desktops 2 and Special Music.

Easy Tokens - Play Metal Slug 3 or Metal Slug 5 on the Hard difficulty setting. Immediately after you defeat the final Boss (when the Boss is going up in flames), save the game, then quit to the main menu once the credits begin. You should get five Tokens. Then, load the saved game file and repeat as many times as desired.

Art galleries - Successfully complete the indicated game(s) to unlock the corresponding gallery:

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: All seven Metal Slug games on any difficulty setting with limited continues.