Metal Gear Solid borrows a good number of gameplay/plot elements from the previous game, Metal Gear 2: Solid Snake. The similarities are numerous, but the most notable ones are:
• The idea of looking on the back of the game's packaging/cd case for a hidden codec frequency. Both contact a female contact that help Snake out on his mission and both are even the same frequency, Spoiler:140.15. Both also get romantically involved.
• The idea of having to change the temperature of an object to turn it into a key.
• The idea of an anonymous source of help contacting Snake, Spoiler:both of which end up being Gray Fox.
• Snake has to run up a long flight of stairs while being chased by a number of soldiers in both games.
• The idea of a 4-man ambush inside of an elevator. The Metal Gear Solid version differs in that the four soldiers that attack are wearing stealth camouflage, which was also taken from Metal Gear 2 as there was a soldier who attacks Snake while wearing Stealth Camouflage.
• A battle with a Hind-D using Stinger Missiles.
• Snake has to battle an operational Metal Gear, and after destroying them he then has to fight the pilot of said Metal Gear in hand-to-hand, as his gear is taken away from him.