Bubbles is an Animal Instinct Awakened Hippopotamus Barbarian, with all the associated bulk. Mechanically, using Animal Instinct Tyrannosaurus because Pathbuilder doesn't know about hippos - the tail attack being reflavored to a stomp, because hippo tails are too small to be taken seriously.
Bubbles is best described as having "golden retriever energy" - super friendly, super outgoing....not necessarily the brightest bulb in the box. He learns, just slowly.
Bubbles doesn't really remember anything prior to his awakening, just that when he became aware there were some humans around who were not very nice, and trying to keep him in a pen. In a fit of rage, he trampled them and managed to break free of the pen.