Jay is a human man with combed over dark brown hair and black eyebrows. He has an angled jawline and stubble on his chin. He presumably is wearing a fake mustache.
He is seen wearing a red sweater, blue overalls, and shoes, presumably all part of his costume for his role as Mario.
Jay is an exaggerated version of his real-life counterpart.
In A Horse Walks into a Rehab, in painting class, Denise compliments BoJack's painting. She says she knows a lot about art because her husband owns a Jackson Pollock. Jameson H., then says her father owns a signed picture of Kevin Pollock. When asked by the therapy horse if he grew up in a home with a lot of art, BoJack sarcastically says, his parents "practiced the art of being terrible parents." The group once again laughs at this.
Doctor Champ tells BoJack he can't joke his way through this, and everyone else is being honest.
BoJack says all the other patients are lying as well. Doug continues wearing a business suit even though he won't get his finance job back, Joan Tripplehorn is really Jeanne Tripplehorn wearing fake glasses, and actor Jay Hernandez is undercover under a pseudonym for a role he is playing. Jameson then says BoJack is right, and the other clients at the rehab facility suck.
BoJack then takes a jab at Jameson, saying she would love to get sober, but her friend McCaitlyn sneaks her water bottles filled with vodka every visiting day. Doctor Champ is shocked to learn Jameson has been smuggling alcohol into the facility. Jameson then blames vodka for being "water colored." BoJack then points out it's her fifth time in rehab and maybe rehab just isn't working.
BoJack further says if anyone checks into rehab more than once, maybe they are a lost cause, or maybe rehab is a money-making industry that does not have people's best interests at heart. He then asks Doctor Champ if that is honest enough for him.
- In Feel-Good Story, Beverly is shown to have had a crush on him as she wished he was her "secret admirer."
- Jay is allegedly at the facility undercover under a pseudonym for a role he is playing.
- In A Quick One, While He's Away, his movie poster is seen on a wall.