Anything this solo friendly needs supporting.
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Trials for One
Solo Roleplaying ICRPG
The Index Card Role Playing Game is an intriguing game for solo players. Right there in the core book (2nd edition pg. 48), it suggests playing through the three trials on your own [that is where the trials in this book's title comes from]. Anything this solo friendly needs supporting. This book is that support.
The core rules do not give any solo rules. ICRPG is not big on rules of any kind. This rule booklet is just 22 pages, mostly examples and support material to help you get started in solo playing if you are not used to it.
ICRPG works for any setting. In the core rules is a fantasy setting and a sci-fi one. I prefer sci-fi, so all the art and my example character are sci-fi. The rules are not setting specific, these work with any game powered by ICRPG, all you need is a d20 and your imagination.
The printed book of this title will be available in 2021, once the printers have resolved their production issues.