Art Gallery
     This  will  tell  you which games are needed to beat to unlock an
art gallery.

Unlockable:        How to Unlock:
Art Gallery 1      Beat Metal Slug
Art Gallery 2      Beat Metal Slug 2
Art Gallery 3      Beat Metal Slug X
Art Gallery 4      Beat Metal Slug 3
Art Gallery 5      Beat Metal Slug 4
Art Gallery 6      Beat Metal Slug 5
Art Gallery 7      Beat Metal Slug 6
Special Art        Beat all Metal Slug games