Overpower in SuperSlam (mentioned on Base of Mountain) and CR is as follows:
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Overpower is a static ability that means "This can't be defended by more than one action card."
8.3.22a If an attack with overpower is currently defended by an action card, an additional action card cannot be added as a defending card to the attack's chain link..[8.5.32]§
8.3.22b If an attack is defended by two or more action cards and then the attack gains overpower, no cards are retroactively removed from defending.
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The Dynasty Release Notes states “Overpower does not prevent additional action cards being added as defending cards through effects (e.g. Amulet of Havencall).” which contradicts the CR.
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Proposing for the Dynasty Release Notes to be updated if possible 🙂