Kay, gather round the fire and listen to a tale of olde.
Once, when people did not think MAGIC would get off the ground, they invented cards, before power levels were introduced.
The creator made the Black Lotus on the first day and saw it was good.
The creator then created the Moxen in the image of the lands, and saw it was good.
He then created the first cycle of cards... The Ancestral Recall being the most overpowered of the five.
After drawing 3 more ideas at instant speed, he then created the Time Walk, and after skipping a day, saw it was good.
Last, the Timetwister was created and completely finished the Power 9.
So you see young'n, that is the story of the Power 9.
Sparknotes Version...
Basically they are a set of cards that are so powerful they are worth a pretty damn penny.
They are on the RESERVE LIST and will never be reprinted outside of promos or tournament items.