Oshawott. I'm nihilistic like that
Sometimes I refer to him as "Oshie" or, more frequently, "Wottie"
However, my brother (though he didn't TECHNICALLY nickname them) calls his Pignite "Porkloinio", his Patrat "Fat Faec", his Pansage "Mojo Jojo", and his Roggenrola "Dented Blueberry".