Demigod’s Wager is a divination card. A set of seven can be exchanged for an Orb of Annulment.
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Demigod’s Wager can be dropped in the following areas:
The Cleansing Light of Basilica Map
The Orb of Annulment is a poe currency item that can be used to remove a random modifier from a magic or rare item.
Vanity drops from the Vaal vessels at the end of corrupted side areas.
Demigod’s Wager drops from Basilica boss (maybe act 5 Innocence too?).
Imperial Legacy drops in Dunes. EDIT: Apparently anything with a desert tileset.
That’s all I know personally.