Can Imposter wear masks of Avatars with pre-game or setup abilities, and if so, what happens?
Yes, you can wear masks of those avatars, and you simply ignore their pre-game or setup abilities since the game has already started by the time you put on the mask. For example: You can use Pathfinder's ability even though your atlas has duplicate sites. You don't get to pick a Unique Dragon as Dragonlord. (Probably not a good choice of masks.) You don't roll for summoning portals as Harbinger. (Probably not a good choice of masks.) Your decks and card sleeves remain as-is for Magician. (Probably not a good choice of masks.)
What rarity are Avatars for purposes of including them in my collection?
What happens if I impersonate the Realm-Eater, use the ability to destroy a site, and then take damage or otherwise lose that mask before I can digest?
The Realm-Eater's ability will have created an ongoing effect which immobilizes you, and can only be removed by activating the 'digest' ability. If you lose that ability, you cannot remove the immobile effect. Be careful!
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