Everything started when I got the idea of playing Sword & Backpack RPG in solo mode using Bivius.
S&B uses 1d20 so it was perfectly natural to use a d20 as the B.R.O. in Bivius.
I’ve been thinking that 1d20 has many faces 😀 and I could use this fact to create a more detailed oracle (Bivius has only the Rule # 8 for a binary Y/N answer).
The most natural thing for me was to convert The FU oracle (a d6 table) in a d20 version but with many more variations. I thought of a very famous d20 oracle toy, (http://www.ask8ball.net/) but its answers were not suitable for an rpg: too vague or inconclusive. A quick Google search led me to a list of English conditionals.
I took some that seemed fit (if, while, unless…) and added other ones.
However, I wanted an oracle that was not too rigid in the answers, but adaptable to the situation.
For this I have inserted the conditional in parenthesis as a simple suggestion after the Yes / No responses, if not fit you simply ignore it and use the basic Y / N response.
Now I had a very detailed oracle for questions to be answered during the game, I had Bivius for the rest and S&B as the starting point.
But Bivius is a complete RPG (it has standard RPG rules plus an integrated solo engine), I had seen that the d20 had great potential for the variety of possible outcomes with only one roll.
I then thought of creating a real self-contained Game Master Engine (GME) but still compatible with Bivius and S&B, What could be the other indispensable tables?
To create the story I liked the Bivius system of the two options but having 1d20 available instead of a binary random generator I could also vary the chances of the two options as other games had done. I’m a roleplayer of d6s and d10s games, I’m used to thinking about the odds in terms of percentiles, real-world probabilities are measured in this way as well.
Calculating the odds between two options by rolling dices of different type or using a dice pool is not for me, I wanted a simpler but precise system, a way to calculate the odds in percentiles, roll one d20 and get immediately the selected option.
Each number of a d20 has a 5% probability, it was a great way to calculate the odds that an option would take place. The other option would have occurred otherwise.
To get a simple but complete system other than the oracle and the option selector, I only needed two more things : a scene generator and a NPC generator. With four d20 tables there is enough to run a solo RPG adventure.
I used Zathrum in some short adventures and it all went well!