ok, this is an idea I had for creating a co-op survival horror/other game where normally the fact you have a partner to back you up and accompany you would take away a lot of the fear, tension or atmosphere.
Assume the two characters have a method of contacting each other, basically a radio. and that's the only direct contact with each other for most, if not all of the game, with puzzles in one area having solutions or hints in the other, like one character mentioning a malfunctioning lock in one area gives the other the idea to get past their own trouble, or one having to use turrets to defend the other as they try to get through/wait for a door to open. So while the two are not there with each other, they are affecting each others progress.
Assume the two characters have a method of contacting each other, basically a radio. and that's the only direct contact with each other for most, if not all of the game, with puzzles in one area having solutions or hints in the other, like one character mentioning a malfunctioning lock in one area gives the other the idea to get past their own trouble, or one having to use turrets to defend the other as they try to get through/wait for a door to open. So while the two are not there with each other, they are affecting each others progress.