obese beast
An overweight beast that has crossed the threshold between general fatness and obesity. Monstrous appetites, disproportionate dimensions, and a craving for twinkies are all typical characteristics of obese beasts. Mobility is often restricted in these animals and resort to rolling as a form of transportation.
Eric: John stop feeding my already overweight dog
John: Why? It isn't _that_ fat!
Eric: Are you kidding!? It is such an obese beast!
John: Why? It isn't _that_ fat!
Eric: Are you kidding!? It is such an obese beast!