Night after night they cross the featureless wasteland of endless thought deserts.
The Dark Caravan
The bag of these merchants of mysteries and their black camels contains 10 marbles: 1 green, 4 blue, 2 black, and 3 white (tradegoods).
Treasures from beyond an Empty Mind: When selling tradegoods, before sacrificing the tradegood marble, a number of marbles equal to the number drawn for the transaction are drawn from the bag of the Dark Caravan. If at least one blue marble is drawn, the tradegood marble does not have to be sacrificed (the transaction still happens). If no blue marble is drawn, then a randomly drawn marble from the bag of the Dark Caravan has to be exchanged for a black marble.
Image by OpenClipart-Vectors from Pixabay