Today, the "collection" concept has shifted. Platforms like Steam, GOG, and the Epic Games Store sell the games individually or as part of SNK bundles. Where to Find Your Serial Number
To find your serial number:
For the retail releases of Metal Slug Collection (specifically the PC CD-ROM versions), the serial number served a specific function in the installation wizard: metal slug collection pc serial number
– For a completely legal route, buy Metal Slug games on the ACA NEOGEO series (on Steam or consoles). No serials, no DRM issues. Today, the "collection" concept has shifted
Disclaimer: This information is for educational purposes for legitimate owners who lost their key. Circumventing DRM for a game you own is legally ambiguous but often morally defensible. However, downloading full games you do not own is piracy. No serials, no DRM issues