Quoted By:
The giant stone behind the sundial, as well as the stone which the 'ultimate weapon' uses are meteorites. All evolution stones are also meteorites (fire, leaf, etc, as well as Mossy Rock/Ice Rock, eviolite, everstone).
Pokemon are alien in origin and these meteorites affect them for that reason. See Mew, Deoxys is a space virus and the origins of the original dragon form of Reshiram/Zekrom/Kyurem which came from a meteorite crash.
Diancie is the living legend born from the meteorite at the sundial.