How would you put co-op in a metroid game?

@OP This post is why I prefer not to compare games from different genres.  They are NOT comparable and shouldn't be compared. If I were to choose the series that I liked more, it would be the Prime series, but that is were any comparison should stop. If you wonder why I say they are different genre's, let's not talk about perspective and look at core gameplay. What is the core gameplay of halo? Shooting. What is the core gameplay of Metroid? Puzzles and Adventure. They may be in the same perspective, but as long as the core gameplay of both series are what I mentioned they are in different genres. Therefore Metroid Prime is a First Person Action Adventure, while Halo is a first person Action game, or to be more specific First Person Shooter.