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My suggestion: it could offer two different solutions - ultimate death... Or the key is actually an item that provides a one-time safeguard against lethal danger. Example: if the player was going to die, game time is rewinded by 5 actions and he can find a skeleton where he's placed - holding the same key, but with nothing written on it, as it doesn't work anymore.

A time travelling get out of trouble delight, very useful...I wonder if the skeleton should look more alien like for even more twist :)

That would explain how he doesn't fit in the rest of survival island!