Well, uhh... I'm not really an expert on competitive battling, I just take breeding requests.
But if you're going for a Prankster Meowstic you're most likely going to be running some kind of defensive/support set, possibly dual screens with Light Clay.
You might want a Bold nature for that, which increases Defense but decreases Attack, which is a stat you're not using on Meowstic anyway.
EDIT: If there's a competitive expert somewhere out there, maybe he can fill in some holes in my description.