Broad Idea
This is a pretty broad idea and you can or could make literally anything. Thus I'm gonna brainstorm some ideas that I'll mention or talk about. There are some important aspects that we should discuss and consider before though.
PC, Mobile, and Combinational Weaknesses
First of all, combing mobile and computer games we need to know the weaknesses of the coupling as well as each of them themselves. Mobile devices have restricted input, using virtual buttons makes it tedious to control them, the view on the screen can, could or is blocked by the user input when using touch. Phone batteries are still limited, many phones in the current generation do not provide cooling. They can be carried easily in the baggy trousers for example. On the computer side, we have limited transportation. You could use a laptop but that also requires a backpack, laptop bag or some other way to transport that chungus. Coupling them pretty much fixes some issues up above but only to a certain degree. We can now move around playing the game somewhat but we're limited by the phone's hardware. Also, the usage of the phone at home while playing the game on the computer can be annoying or intrusive. So, I'd say that's discouraged. Could make an interesting mechanic in games where you have to multitask between devices though.
The Untapped Potential
The basic idea of many game developers is to get the player to think about the game in their spare time or free time. Thinking about new strategies to come up to try out or solving other problems for example. Using a mobile device you can make an app that is connected with your game to have something for the player while they can't play the main game. This could be mini-games, gamified tasks that give in-game rewards or provide community and theorycrafting features and the biggest thing about this is, that I haven't found one game that implemented this. It doesn't mean it doesn't exist but, hey. Be the first to get it out there.
Examples
One example would be to use the way Pokemon GO! was implemented to make a similar game for resource gathering. Allowing you to gain resources for the main game at the cost of your in-game currency. This gives the player an alternative to do sport, or collect resources while traveling for example.
Another option would be to share and allow communication with the guild chat via an app.
This way people can communicate with each other through your app. This doesn't require the player to download Teamspeak or Discord for their mobile phone or to create a WhatsApp group. Additionally, it's possible to implement unique game information into it that would not be possible to be provided by other apps.
This one pretty much shows that you can make literally anything. Your only limitation is the
imagination... and well... user experience design. Anyways you could also make an app that gives you puzzles for chests or areas that are locked off and you need to open them via a puzzle on your mobile phone for example. You could even implement a wait time, that way you can collect these in-game and then when you're most likely outside the game you can do them in the mean-time.
Conclusion
The basic idea is quite simple here. Make a mobile app that keeps your users busy while not at home being able to play the game. I mean, this is not the most interesting thing for mobile development. It does, however, avoid all the issues that mobile-only game development has for big games. Another post I should address...
