In creating the Parasites transmedia story, it's important for the online game to dovetail with the movie & live events (screenings) in an elegant way. That means not overly complicated, not contrived and not an irrelevant add-on. The movie, events and online game need to offer parts of the whole and yet be satisfying in themselves.
The best approach I'm finding to achieve this seems to be to take an idea through successive iterations of each media. The good ideas snowball - reinforcing their merit with each pass - while single-media ideas melt away.
Note that each media has its own demands. For example, for the movie to work, the audience should allow the director to guide them through the story and in doing so have the drama unfold. Whilst for the game it's the player that finds his/her own drama. Both complete parts of a larger story but the method of engagement is different.