level up during the night holding razor claw
there is a small chance you can catch it in icefall cave on 4 island
First go to summer land then go to the bottom of the city and take the stairs. Then walk until you reach a cave. Next go into the cave and follow the stairs and go through the hole and then through another one after that one and another, and another then go down the stairs.Next go right ten up and go down the stairs.Now go up then left then up and go up the stairs.Next go up the stairs on the left.then go right down left and up there is a sneasl right there.
There is not a certain level it evolves at, but certain conditions that have to be met. You have to give it a razor claw and then level it up at night. Then you get one of the best Pokemon: Weavile.