I propose to slighty change it as followingWR: Mithril is stored at a Haven.
There's indeed no defense possible against a "Neither so Ancient nor so Potent" if Mithril is stored the last turn's org phase (or forelast turn's end-of-turn phase with Safe from the Shadow).WR: Mithril has been stored at a Haven.
It happened to me at Lure XV, but I won't denounce here opponent