When Dances Up Earthquakes plays a Major Power via Unlock the Gates of Deepest Power, what happens if you make that Power Card impending?

When Dances Up Earthquakes plays a Major Power via Unlock the Gates of Deepest Power, what happens if you make that Power Card impending?

If you choose to Forget the Power at end of turn, then nothing useful happens: you make the card impending, then Forget it when the turn ends without ever using it.
If you choose to pay with Energy, Begin a Dance of Decades lets you pay any amount of Energy – even more than the amount you'd normally have to pay. This may be advantageous if you want reduce the time it will spend impending. The impending card will then come into play on a future turn, like impending cards normally do. It won't automatically gain all elemental thresholds on that future turn, and it won't have an energy discount, since those effects of Unlock the Gates of Deepest Power expire when Time Passes this turn.