Originally a Nintendo DS title, it was the only mainline Metal Slug that had never gotten a proper home arcade release. To play it on his big cabinet monitor, he needed a miracle: a ROM that worked with MAME, the arcade emulator core on his Recalbox.

Many 2021 Recalbox users opted for Metal Slug XX over Metal Slug 7 for this very reason.

Recalbox is a powerful front-end, but since Metal Slug 7 isn't an arcade game, it won't work if placed in your mame or neogeo ROM folders.

To play it on a in 2021, you generally have two main paths: 1. Use the Nintendo DS Core

He walked to his arcade cabinet. It was a Frankenstein thing—an old gutted Neo Geo cabinet, a second-hand LCD, Sanwa joysticks. He pressed the power button. Recalbox’s splash screen—a cute pixel raccoon—winked at him.