Yig (who came with Forsaken Lore) has the following mystery (emphasis mine):
Crown of the Serpent wrote:
When an investigator would gain an Artifact, he may gain the serpent Crown Artifact instead.
At the end of the Mythos Phase an investigator that has the Serpent Crown Artifact may attempt to break the crown's hold on the minds of those it has dominated (test Will - 1). If he passes, he may spend Clues equal to (# of investigators) and discard 2 Ally Assets to solve this Mystery.
In this case, advancing the Mystery would place a clue on the card in advance thereby reducing the number to be spent later.
On a side note, this is one of the toughest mysteries, in part because the Serpent Crown Artifact has a reckoning effect that says "discard an ally".