Solo games

Technically there is math that can be done in D&D 5e that is intended to give you a balanced encounter for any number of PCs. A single 1st level PC is going to be fighting lots of rats and maybe a lone wolf. Or at least that's what I remember...animals are the primary creature the MM has that works for a single PC. A Bandit would be a difficult challenge if my memory serves...but that makes sense that a one-on-one deadly fight with another demi-human should be taxing.

What Maskcot said works with Pathfinder as well to by making use of the CR (challenge ratings) for encounters. A Level 1 Fighter who has a CR rating of one would be equivalent to something like 4 Kobolds, for example. It can be a bit clunky, but it's an effective system.

I've made gestalt rules for 5e to support a solo game (for each character level the player has, they get 3 class levels and must have 3 distinct classes; basically it's three characters rolled into one body. Proficiency bonus is based on character level, and the PC gets two initiative slots). It worked fine, basically makes 1 character approximate a party of 3, but there was a bit of learning to get it going.

@Candi, would Legends of Ilvaria support solo play? :-)

It's based on Wushu, and is story-driven (the dicing is meant to be story-guiding more than determining), so it certainly would be fine at solo play.

Pathfinder has challenge ratings down to 1/10th so anything on the 1/4 scale would be doable for a 1st level character alone. Here is a link:

http://www.d20pfsrd.com/bestiary/-bestiary-by-challenge-rating/-bestiary-cr-1

Oh...I just remembered QAGS. It has been years since I read the book, but from what I remember it was fun and quick and the GM could literally skew things on the fly. You had a few stats and rolled under them on a d20 and that was it. You could play literally any game genre.

I ran a game based on the Simpson's Treehouse of Horror story where a witch turned everyone into the costume they were wearing...at a zombie survival run. My friends knew we were playing an RPG, but I started a conversation about what costume they themselves would dress up in if money were no object. So when I handed them character sheets and told them to stat their costumes...they were pretty thrilled. So the PCs were runners dressed as not-zombies and gained super powers based how they chose to dress. The zombie hoard tried to eat their brains, they killed the evil witch, a good time was had by all.

That game could have been a single player game. and QAGS stands for Quick Ass Gaming System, so you can look it up.

First, to answer the question, it's between CR 1/8 and 1/4. 1/8 will be on the easier side, 1/4 on the harder side. Which is a lot of animals, into demonspawn like Dretches, as well as some low-level inhumans like Kuo-Toa and Troglodytes.

5E makes this really easy to figure out, which is something I discovered recently and love. If you look at the "Designing Encounters" section in the DMG, and look at the XP budget thresholds, it tells you how many XP you can spend to generate an easy/medium/hard/deadly encounter for your party, broken down by character level. The way they suggest you use it is adding together all your characters' levels and running the numbers from there--but if you only have one PC, then you can just use the numbers they give you on that table, keeping in mind a 1.5X multiplier for a small party.

So, for instance, it says for every level 1 PC in your group, you can spend 25 XP to generate an Easy encounter, 50 XP for a medium, or 75 XP for a hard. That means you can throw 50XP at a level 1 PC for something that's harder (as it multiplies out to 75XP), or 25XP for something on the Easy-Medium side.

I really like 5E for Duet games, I think it's (somewhat unexpectedly) a great game for them.

Thanks for that @jeffstormer!
@JoHoover if I ever decide to run Pathfinder, that is a great resource.
@Maskot QAGS sounds like a lot of fun.

There's a podcast called Discern Realities that discusses Dungeon World and at the end does a "comic strip" Actual Play, by which they mean a 10ish minute segment of gameplay where the one host runs the game and the other plays. It's been interesting, both for examples of player narrative authority and playing 1-to-1.

I've been looking for some more solo advice, I'm very intimately familiar with The Cypher System, and that's what the other player wanted to play, but I haven't played much one on one with it and am thankful for all the advice here.

I used to have a website that had weekly advice on solo games, but I lost the link. Does anyone have any interesting mechanics they have used for solo play?

You might be interested in this... RPGBot.

Saw your post and got the game to play at home with my brother. I can confirm its good. The player doesn't have complete freedom, but I don't think they are supposed to. I feel like it's supposed to be like a nightmare or dream. Where they can influence things slight, yet their fears and stuff guide the story. It was spooky in the right atmosphere. Dimmed lights, ambient scary music, physical pictures of unsettling places. I'd do some prep before playing for a better experience. Works well for a short one shot.