In addition to running campaigns on Roll20, I also run a game at home with my daughter (10 years old as I write this). We’ve been making our way through the 5th Edition Starter Set adventure, Lost Mine of Phandelver. Of course, running with only one player-character requires a few changes to the normal approach to running a game.
- Nerf the NPCs. This should be fairly obvious, but in addition to reducing the size of encounters, I also generally don’t allow critical hits from the NPCs. I tried reducing their hit points, but that didn’t seem to increase the fun that much.
- Guide the player to an appropriate class and build. A Cleric built for buffing and enhancing party members will not shine in a solo campaign. She’s been running a Rogue and that has worked out well, with the ability to choose her fights and then hit hard and quickly.
- Focus on things other than combat. We’ve had a good time enjoying the roleplay rather than just the stabby-stabby. For a pre-teen, I can already see this working on several levels for her, because she’s learning more about interacting with different sorts of people and with different sorts of goals than she typically would have in real life.
- Find out what’s fun for the player. This applies to any campaign, naturally, but especially so in solo campaigns. In traditional party-driven play, part of the fun comes from the interaction among the players themselves. But here, that doesn’t exist and the world really does revolve around her (at least in some ways).
- Rule of Cool trumps everything. Since you don’t really need to worry about balancing power levels, let the character be extra awesome. Maybe that means fudging a roll here and there, or (for some people) that might mean allowing additional features and proficiencies and whatnot.
See what works for you, but this is what works for us. A solo game provides a far different experience than what you might normally get: much more emphasis on storytelling and individual action, plus a tightly focused adventure. I hope you have as much fun as we do.