Mox Jasper (Serial Numbered) - $1,500 The top-earner from Tarkir: Dragonstorm (a great set, by the way), Mox Jaspers serialized version is numbered up to 500, pushing the value up to around $1,500
Meanwhile, the Floodborn Lady Tremaine Imperious Queen is also an effective card that can be leveraged to debilitating results
Chart shows the price of Fennekin #80 at the end of each month going back as long as we have tracked the item.
The secondary market for single cards doesnt impact the publisher at all
So thats like, one of the best mill payoff cards, allowing you to cast spells for cheap
1 Atraxa, Praetors' Voice The Proliferation Queen Speaking of Proliferation, Atraxa can quickly turn the tide in a battle just by sitting out on the battlefield for a few too many turns