This is a StoryNexus content design pattern. Other patterns can be found on the Content Design Patterns page.
Think of a big snake that's swallowed a rabbit – thin at either end, but thick in the middle. Pythons are usually based on Sometimes cards. The tail of the Python is an storylet that appears once; if you play it and succeed, you get a Mark of Cain quality that unlocks the bulge. The bulge is a number of cards that can be played in any order, each of which increase the token quality. Success at these will advance the narrative, but in a nonlinear way; eg investigating a puzzle, you could interrogate different people in whichever order you choose, or head to the library, or examine the crime scene. Every success in these cards increases the quality, usually by the same amount. The head of the python is one final storylet, unlocked once the Cain token reaches a high enough level; success at this wraps everything up and finishes the story. The head storylet could be a test on the Cain token quality, in which case it should be possible to go back and increase the bulge storylets a few more times to increase your chances.
- Charge a toll to play each stage.
- Put multiple branches on the last storylet, so the player can choose the ending. This variant is a Hydra.
- Reset the quality at the end, to make the whole thing replayable.