He originally wanted him to be a Stank Ass #6, but chose to name him Priority Mail instead. At the end of Episode 71, he said he was going to tame a white cat and have him and Priority Mail fight. In Episode 72, when he finally tamed and named the white cat Stank Ass #6, he described them both as "Yin and Yang" because of their colors matching the symbol. When Nova was going to find and tame a Panda, he noticed that Priority Mail was gone. His first speculation was that Priority Mail drowned himself, then he speculated that Priority Mail climbed to the top of a mountain. Because of this, Sly and Seamus joked that Priority Mail was sent somewhere else because of his name.
At around 12:40 in Episode 72 of the series, on Nova's Channel, he notices a fox fighting an unknown creature on the roof of their house. Unbeknownst to him, the unknown creature was Priority Mail. Priority Mail did not survive the fight with the fox.
Priority Mail had apparently faked his own death, as he returned in Episode 74.