>>715920707
>maybe two playable characters (Samus, and Sylux?)

This would be great if you progress through the game as both of them and the actions of one affect the other.
It would be interesting to have optional things that you can do as Sylux that would obstruct Samus's play, next to stuff like needing both to complete puzzles, like releasing monsters in a room that would otherwise not have them.
Next to the collection clear score you'd have something like a clear score for Sylux for how many things you had Sylux do to block Samus' progress as an incentive.