7. The Function Of The Cyborg Ninja Skin
The old-school PS1 skins for Solid Snake and Grey Fox are fun purely for fan service, but the latter actually has a hidden ability - faster running speed. After the skin unlocks near the close of the game, developing and equipping it will bolster your run-speed to far faster than the default animation. In addition, the Raiden skin you can unlock by S-Ranking all missions is faster still, and even comes with Metal Gear Rising's aesthetic that makes Raiden's feet crackle with electricity - which you can use to sprint-knockout any guards in your way.