It is unknown what Erica looks like or what her everyday attire is. It is implied, however, through various comments from Mr. Peanutbutter and BoJack, she is seriously disfigured.
The audience becomes aware of her existence through one-sided conversations and mentions by other characters.
Whilst being occupied with something else, Mr. Peanutbutter will get distracted in some way by Erica, abruptly exclaiming: "Erica!," which is one of the series' longest-running recurring gags, premiering in the first episode.
Little is known about Erica, only small snippets of her life can be gathered, from the few statements when someone is talking to or about her.
Erica might be either not a US citizen or a felon since she can't vote in national elections. Mr. Peanutbutter's numerous comments imply that the possible crime might have involved minors, given that Erica can't be at Todd's Disneyland because it's filled with children, and she was seen with a child-sized coffin.
Episode Number: S01E01
Mr. Peanutbutter's Exclamation: "Erica! Get outta here with that face!"
Episode Number: S01E01
Situation: At the quinceanera at BoJack's house, BoJack and Mr. Peanutbutter are making (reluctant) small talk.
Mr. Peanutbutter's Exclamation: "Erica! How are you looking so beautiful? I'm furious!"
Episode Number: S01E01
Situation: While Wayne is interviewing Mr. Peanutbutter for his Buzzfeed article, Mr. Peanutbutter gets a call from Erica.
Mr. Peanutbutter's Exclamation: "Erica! I don't have time to be charmed to death right now!"
Notes: It was presumably Erica who told Mr. Peanutbutter over the phone that it was "Burritos-as-big-as-your-head-day" at El Taco Loco.
Episode Number: S01E06
Situation: Directly after Mr. Peanutbutter proposed to Diane privately, he reveals to her that he had a surprise engagement party planned.
Mr. Peanutbutter's Exclamation: "Erica! Did you hear she said yes? Come in here! Alright..."
Episode Number: S01E09
Situation: Mr. Peanutbutter is recalling a story of how Erica gained a friend at his rehearsal dinner.
Mr. Peanutbutter's Exclamation: "Long story short, Erica did have to lose the foot. But she gained.. a friend. Sorry, kinda went off on a tangent there."
Episode Number: S01E12
Situation: At the after party of the Golden Globes, Mr. Peanutbutter and BoJack are conversing.
Mr. Peanutbutter's Exclamation: "Erica! Is that you? Who let you out of the burn ward? Get over here, you!"
Episode Number: S02E02
Mr. Peanutbutter's Exclamation: "Erica! You can't be here! This place is filled with children!"
Episode Number: S02E07
Situation: In the 1994 flashback, a bitter Katrina leaves an indifferent BoJack and an embarrassed Mr. Peanutbutter to join Erica for drinks.
Katrina's Exclamation: "Erica! Throw me a raft! I'm dying."
Episode Number: S02E12
Situation: Mr. Peanutbutter is socializing at a party while Diane is brainstorming new app ideas.
Mr. Peanutbutter's Exclamation: "Erica! Where did that tooth come from?!"
Episode Number: S03E02
Situation: In 2007, Mr. Peanutbutter is hosting a fundraiser for the John Edwards campaign for President.
Mr. Peanutbutter's Exclamation: "Wha...? Erica! You know you're not allowed to vote in national elections!"
Episode Number: S03E10
Situation: Mr. Peanutbutter pulls BoJack out of his pool, who thanks him and tells him Erica was looking for him.
BoJack's Question: "Hey, did you see Erica earlier? She was looking for you earlier, with her good eye. Her other eye was looking at the stars!"
Notes: This is the second time somebody other than Mr. Peanutbutter acknowledges Erica. It is probably inferred that Erica has strabismus.
Episode Number: S04E07
Situation: Mr. Peanutbutter apologizes to BoJack for not admitting him to his fundraiser party for his campaign for Governor.
Mr. Peanutbutter's Exclamation: "Erica! Look at you with the right number of ears!"
Episode Number: S05E02
Situation: At his housewarming party, Mr. Peanutbutter is awkwardly talking to Diane after their divorce.
Mr. Peanutbutter's Exclamation: '"Erica! What are you doing here with a child-sized coffin?"
Episode Number: S05E08
Situation: Mr. Peanutbutter is promising Katrina that he won't leave her alone at BoJack's 1993 Halloween party.
Mr. Peanutbutter: "But I will not leave your side agai—Oh, my god, is that Erica?!"
Katrina: "No, no, no, please don't go talk to Erica."
Mr. Peanutbutter: "Katrina, Erica doesn't know anybody else at this party. It would be rude to leave her all by herself."
Katrina: "Well, can I at least come with you?"
Mr. Peanutbutter: "You know Erica can't talk to two people at once on account of her split-brain procedure."
Mr. Peanutbutter: "Erica! the costume! Where did you find such a hideous—? Oh, my mistake. I'm so sorry."
Notes: This is the first time more than one character acknowledges Erica in the same scene.
Episode Number: S06E16
Situation: BoJack and Mr. Peanutbutter are in the way of Princess Carolyn wedding and BoJack feels insecure about being around people at the wedding. Mr. Peanutbutter reassures him and promises he won't leave BoJack alone unless he encounters Erica.
Mr. Peanutbutter: [...] "And if you wanna stay, I'll stay there with you. I will not leave your side."
BoJack: "You sure?"
Mr. Peanutbutter: "Of course. I'm here for you buddy. No matter what. Unless I see my good friend Erica and get distracted by some noteworthy aspect of her character presentation, but BoJack! What are the odds that would— "
Notes: It isn't shown when Mr. Peanutbutter greets Erica, but it's implied.