Duel Decks have historically been pretty hit-or-miss
So, if I wanted to attack with it, my opponent cant block it with cards like [c]Goldspan Dragon[/c] or [c]Burning-Rune Demon[/c]
Seven mana to transform this into Hydaelyn, the Mothercrystal is a lot, but well worth it
And who gets credit for creating it
Typically, it gets played for its cycling + madness cost ala Ichor Slick from TSP Limited and flashes back, but it has surprisingly high flexibility for such a good card (note that you cant buy it back when its being flashed back as it gets auto-exiled, but you can do things like cycling + madness + buyback if the game goes long)
Number Ten For a brief moment, Vorapede was actually a fairly reasonable card value-wise