PSP and PS Vita compatible, Metal Slug XX will be free starting tomorrow for PlayStation Plus subscribers, according to the PlayStation Plus official blog. As a part of the PlayStation Plus Instant Game Collection Metal Slug XX will be available for a short time for free versus the normal $19.99 price tag.

Metal Slug XX is an upgraded version of Metal Slug 7 on the Nintendo DS and on top of the core game adds mini-games and a co-op mode. Load up your weapons and get ready for the bullet storm.