Metal Gear Solid, released as Metal Gear: Ghost Babel (メタルギア ゴーストバベル, Metaru Gia Gōsuto Baberu) in Japan and Asia, is a 2000 stealth action game produced by Konami for the Game Boy Color. Named after the 1998 PlayStation game of the same title, the Game Boy Color version of Metal Gear Solid (or Ghost Babel) is not a conversion of the previous game, but an original game produced specifically for the portable platform. The story of Ghost Babel is not set in the same continuity as Metal Gear Solid, but instead serves as an alternate sequel to the events of the original Metal Gear, set seven years after Solid Snake's mission in Outer Heaven. It is not part of the main canonical timeline of the Metal Gear series.

Ghost Babel follows the overhead 2D format previously used in the 1990 MSX2 game Metal Gear 2: Solid Snake while adding a few new elements introduced in Metal Gear Solid. As with previous games in the series, the objective is to infiltrate the enemy's stronghold while avoiding detection from guards or surveillance systems. The player can acquire numerous items and weapons to help them fulfill their mission. One difference from the MSX2 games is that the screen now scrolls when Snake moves throughout a single area instead of using flip-screens. Moreover, all the characters in the game now move in eight directions, allowing both, the player and the enemies, to move diagonally in addition to the four cardinal directions. Snake now has the ability to flatten himself into walls like he does in Metal Gear Solid. By flattening himself, Snake can move across the wall (allowing him access to tight passages that are not accessible by walking), scroll the camera behind his position to scout the area ahead, or knock the wall to lure nearby enemy soldiers. Depending on the difficulty, the number of punches required to defeat an enemy soldier differs and in the higher difficulty levels, the enemy soldiers will be knocked unconscious for a while after the first series of punches instead of simply being defeated. Crawling is now assigned to the Start button (instead of pressing two buttons simultaneously) and the changing of weapons and equipment is done on the main game screen rather than on separate sub-screens. Like in previous installments, the player communicates with various allies via a wireless communication device (the Codec), which is also used to save the player's progress.

Unlike the console installments, Ghost Babel uses a stage-based structure, with a total of 13 stages. After completing a stage, the player's performance is graded from "Terrible" to "Excellent". Previously completed stages can be replayed to improve grades. After the Story mode is completed, a "Special" game mode becomes available where the player can replay these same stages, but with new objectives (such as collecting FOXHOUND emblems or completing the stage without being seen). Other additional game modes includes a VR Training mode, where the player can test their sneaking and shooting skills in over 180 missions (some of them based on missions featured in Metal Gear Solid: VR Missions), and a 2-player Vs. Battle mode accessible via the use of a Game Link Cable and another Game Boy Color with a copy of the game.