Metal Slug XX, compatible with both PSP and PS Vita, is this week's new recruit for the PlayStation Plus Instant Game Collection. PS Plus subscribers can grab SNK's run-and-gunner gratis starting tomorrow - the usual asking price is $20. Metal Slug XX is an altered version of Metal Slug 7 on the Nintendo DS. It features additional ad-hoc co-op and mini-games on top of the core DS game. The series is known for its expressive sprites, powerful weaponry, insane boss battles and blatant disregard for bullet rationing. Source: PsBlog