Well, It obviously has 31 IVs in HP, Attack(won't really do anything lol), SDef and Speed.
I think you should use a Special Attacking set since it has a Modest Nature.
First, evolve your Clefairy. Then, proceed to use this set.
EV train 252 HP, 4 Defense, and 252 Special Defense.
Clefable @ Leftovers
EVs: 252 HP / 4 Def / 252 SDef
- Calm Mind
- Ice Beam