This Seeking Tech tutorial will explain how you can unlock the “Mostly Dead” trophy and achievement in the Master Collection version of Metal Gear Solid 3: Snake Eater.
This will unlock when you “use the Fake Death pill.”
To get this, you need to follow the video and text guide below:
Play through the beginning of the game until you get your backpack. You should then get a codec call that explains how you can use the Fake Death Pill.
Afterwards, bring up the equip item menu and then scroll over to the Fake Death Pill. Press the button to use it, and the Mostly Dead trophy and achievement should unlock.
You can then use the Revival Pill to bring yourself back to life. It should be notice that the Fake Death Pill is helpful when escaping the prison cell, in addition to certain boss fights such as The Fear.