Humble Bundle SNK Weekend Sale
https://www.humblebundle.com/store/promo/snkweekend/
For the whole weekend (August 14th to August 17th) save up to 50% off all current SNK titles on Steam! That includes Metal Slug, Metal Slug 3, Metal Slug X, with King of Fighters XIII, King of Fighters 98 Ultimate Match Final Edition and King of Fighters 2002 Unlimited Match!