Gentle is the best nature. You should only use goodra against special attacks not physical and Céél it does not have very good defense. it also benefits a lot better from calm than bold. I think it should use both special and physical attack because it has a good and wide physical move pool. Many of its strongest moves are physical.
Pokemon HeartGold Friend Code: 1505-6450-3046. Pokemon White Friend Code: 0820-3178-9794. Pokemon Black 2 Friend Code: 0004-2110-3564. Pokemon Y Friend Code: 1418-6931-6470. (3DS)