We broke it down here
Before you know it, youll find yourself desperately tearing open pack after pack, scrutinizing the rare cards, and sizing up what you can do with the ones you dont like
Time to look up horrors in Modern to make sure your creatures don't get returned with those controlled by your opponent
On the flip side, with Once Upon a Time, two Horizon lands, a man land, and a utility land, you are looking like you are closer to 13/39 lands and safe on flooding
I should have seen the writing on the wall with Dunsparce, they usually don't print such fantastic ability support without something on the wings, and the fact that there wasn't a meta colorless deck in format should have been a clear signal that they would print something like this
Other mana sources require tapping (for example, Llanowar Elves, or Mox artifacts), others require sacrificing (for example, the "Black Lotus" from the alpha/beta edition), and so on