Multiple copies of chase cards

[Jamineal]

After seeing a few of you guys' decks, I see that you have multiple Mox cards and others that I only get one of. Any time I've been offered a duplicate card, I've never seen them on the list. Am I just crazy, unlucky, or crazy unlucky?

[drool66]

There are a few high-level enemies who, after you defeat them, may offer to duplicate a card in your deck.