The Dust decks are used only when playing with Quachil Uttaus as the Ancient One. They can continually raise the threat to the current first player and can cause him to be devoured without any combat.
Using the Dust Decks
Shuffle the three dust decks at the start of the game and place them face down on the sheet for Quachil Uttaus.
At the start of each turn, the first player must either spend 2 clue tokens or draw a card from the lowest-numbered dust deck that still has undrawn cards in it.