Use once as a free action: flip a fair coin. Heads: your king is gilded, purely cosmetically, forever. Tails: nothing but a sheepish flash on your king.
You draft Fool's Gold in either mode. Free action: you choose when to use it, and it resolves without costing your turn.
As a item card, it is a one-use consumable, drafted in either mode.
“Worthless, gorgeous, and yours.”