I would put this at rare, even though the trigger condition rarely happens in games. That's because the card's effect isn't mythic-y. It doesn't make a big splash.I like how this dances around in new design space. =) It's similar to how I want there to be a condition on a card that triggers off of you taking extra turns.
A card that triggers off of extra turns would be interesting... though pretty limited in use! If you're taking extra turns, you're most likely already winning anyway. :p
Interesting effect. Quite possibly powerful, but I can't imagine it being too powerful - it essentially converts a land drop, and the opportunity to cast sorceries, into two cards (given that you would have drawn a card in the draw step).Not mythic, as Bradley said, but very good indeed.