Cryptolith

Cryptoliths or Cluestones are stone artifacts created by the planeswalker Nahiri on the plane of Innistrad. They are scattered all over the landscape.

Tamiyo's alchemical analysis on the moorlands' cryptolith formations showed a high surface hardness, and a directional energy field along a twisting axis. The strength of the internal lodestone field in each monolith is able to distort local field lines and poles. The scattered formation caused a net migration of Innistrad's pole to a location just offshore of Nephalia, the Drownyard. The disruptive properties of the stones appear to warp the flow of mana through the region, with potentially severe effects for beings composed of raw mana — particularly the angels of the plane.

The cryptoliths are actually leystones shaped to bend Innistrad's leylines to Nahiri's will, and to summon Emrakul. After Emrakul had been summoned, the cryptoliths directed the Ley Lines at the strongest concentration of life on Innistrad, the city of Thraben.