Snake's Revenge (also known as Snake's Revenge: Metal Gear 2) is a stealth action-adventure video game produced by Konami for the Nintendo Entertainment System in 1990. It is a stand-alone sequel to Metal Gear that was released in North America (under the Ultra Games brand) and the PAL region following the international commercial success of the NES version. Much like the NES version of the first Metal Gear, the game was produced without the involvement of series creator Hideo Kojima, who went on to develop a separate sequel for the MSX2 titled Metal Gear 2: Solid Snake, which was released later during the same year in Japan. As in the original Metal Gear, the player's objective is to infiltrate the enemy's stronghold while avoiding detection from enemy soldiers or surveillance devices. To fulfill their mission, the player must collect a variety of weapons and equipment, such as firearms, explosives, and rations, as well as card keys to access new areas. If the player is discovered by the enemy, the game will go into an alert phase, causing enemy soldiers to enter the screen and attack the player. The player must defeat a certain number of enemy soldiers to return to the infiltration phase or go to a different floor or area. In some cases, particularly when a guard sees the player and only a single exclamation mark (!) appears over his head instead of two (!!), the player can also escape the alert phase by simply moving to the adjacent screen.