Pinkie Pie is a Time Lord · 5:15am Nov 3rd, 2011
It explains how she can just 'appear' anywhere at any time at the most comically convenient moment possible.
Think about it. All those strange places she pops out of? TARDIS with functioning chameleon circuit allows her to appear in the strangest of places, like say, a bucket of sponges despite it not being physically possible for her to fit there.