Nature Power is a Normal-type move. Its move varies depending on the climate and the place you are.
As of X & Y:
It becomes Tri Attack inside buildings, Power Gem in caves and mountains, in deserts and roads it becomes Mud Bomb. In grass, it becomes Energy Ball, Blizzard in snow, and Hydro Pump' in water. 'Moonblast in Misty Terrain, and Thunderbolt in Electric Terrain.
As of Black & White:
It becomes Tri Attack in buildings, Rock Slide in caves and mountains, Earthquake on deserts and roads, Seed Bomb on grass, Blizzard in snow, and Hydro Pump on water.