Metal Slug X is a heavily modified and upgraded version of Metal Slug 2, widely considered by fans to be the most polished and frantic entry in the classic trilogy. SNK utilized the Metal Slug 3 engine to completely eliminate the slowdown issues that plagued the second game. They also changed the levels' time of day, rearranged enemy placements, and added a massive arsenal including the Iron Lizard and Drop Shot, along with supercharged versions of classic weapons. The game is celebrated for its dark, absurd humor and relentless co-op action. The original AES cartridge is a highly coveted collector's piece, fetching high four-figure prices due to its limited domestic release in 1999.