Cresselia doesn't seem like it's really doing much for your team besides Thunder Wave. Since you also have three Ice weaknesses, either a Wide Guard user or something that can take out Scarf Abomasnow might be more useful.
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Black 2 FC:
My Pokécheck Pokémon
RNG is kind of like firing a gun. Why shoot blindly in every direction until you're lucky enough to hit the target when you can just take the time to aim properly and hit it with one shot?