He died when Rose was 4 1/3 years old. Rose, being a fan of psychiatry, often held psychoanalysis sessions with Jaspers while he was alive. During his last session with her, he told her the stunning secret that would haunt her mind for years to come: MEOW. This seemingly insignificant phrase unlocked a genetic code in Rose's subconscious, which she spent years scrawling on her walls not knowing what it meant, and then suppressing the memories of it, until her dream self woke up. She wrote the same sequence in one of her journals, which Dave replicated with his Alchemiter. In Act 4, the Draconian Dignitary steals this code from Dave's home and uses it to create Becquerel.
Unfortunately, after he told her this secret, Jaspers disappear[ifi]ed into thin air, and would be gone for a couple weeks, at least from Rose's perspective.
What Rose doesn't realize is that Jasper's disappearance is the result of one of Roxy's appearifier experiments teleporting him to post-scratch Earth.
Jaspers lived withRoxy Lalonde for a time, and was renamed Frigglish, a character from Complacency of the Learned. Over time, Jaspers would lose hope of seeing Rose again, and contented himself with living with Roxy, though he never loved her quite the same.
Eventually, Roxy decides to appearify Colonel Sassacre's Daunting Text from Jane's room as part of an experiment to prove that she can do such a thing. As she prepares to appearify the book, God Cat appears in the middle of Roxy's room, startling and angering Jaspers. Jaspers hisses at God Cat and pounces at it, but it teleports away. Roxy then appearifies the book, which falls on top of Jaspers, crushing him flat. This seems to have been previously foreshadowed at the introduction ofColonel Sassacre's Daunting Text by saying that the book would kill a cat if it were to be dropped.
Back in the pre-scratch universe and a couple weeks later from the perspective of Rose and her Mom, his body was found in the river that runs through the manor. Rose cared for Jaspers enough that she asked her Mother to hold a funeral for him. Her mother, naturally, went lavishly overboard with the proceedings, giving Jaspers to a taxidermist to prevent decomposition, fitting him with a new tiny suit, placing him in a coffin meant for an infant, and sealing him in a Mausoleum in the backyard of the manor while wearing an all-black version of her suit. Rose perceives this process as a passive-aggressive gesture, but given Roxy's love for cats Rose's Mom probably intended it as a sincere gesture. This is also in line with her getting severely drunk and passing out after the funeral.
Interestingly, underneath the dais in the mausoleum is a secret door leading to an underground passage to the SkaiaNet Laboratory next door. It is opened by entering a password into a keypad in Rose's house.
Jaspers is responsible for Rose's desire to play Sburb, as Jade predicts that the game will allow Jaspers to return to life. Rose tells herself "it's pretty much all his fault you're in this mess in the first place", indicating a stronger desire to revive Jaspers than she let on, initially describing her feelings about the animal as "lukewarm".
Rose tries to use the Appearifier located in the Laboratory under her house to retrieve Jaspers from the past, hoping to close some sort of double time reacharound, but instead causes the machine to Paradoxify. The resulting green goo is sampled and used by a nearby Ectobiology apparatus, which proceeds to clone a small, two-headed fetal kitten from it. Rose finds another mutant kitten, this one with four eyes, which she names Vodka Mutini, or Mutie for short.
The fact that Jaspers was sent to live with Roxy is unknown to Rose, as she was unable to track him with the Appearifier during the week he was missing.
Jasper's body is accidentally transportalized to Rose's Mom's room but is brought back and re-captchalogued by Rose before she leaves in the same way.
Jaspersprite
Rose Lalonde's Kernelsprite was initially prototyped with Jaspers, and Dave prototyped it with the Eldritch Princess. Jaspersprite is shown to be very reliable, as it grabbed Rose with a tentacle to rescue her from a fall. It was hinted that Rose would prototype the sprite with Jaspers after Jade mentioned Sburb might be able to bring Rose's dear cat Jaspers back from the dead. Notably, it was prototyped twice before it entered The Medium. Interestingly, Jaspersprite initiates direct physical contact to save Rose, whereas the Nannasprite uses indirect means.
After its first prototyping, Jaspersprite appears as a disembodied cat head surrounded by an orb of light, like John's harlequin sprite. Between its double prototyping and Rose's entry in the Medium, it has the full sprite body still surrounded by the orb of light. When Jaspersprite is seen again in the Medium, the orb of light is gone.
As Rose prototyped twice before entering the Medium, the changes undergone by the denizens of the Incipisphere were more drastic: the opening to Act 4 shows new types of imps taking on all possible properties; Cat, Cathulu, Princess and even some Cathulus and harlequins wearing Jaspers' suit. Like all sprites, Jaspersprite can talk, although he prefers to just make cat noises. He seems to be privy to a lot of important information, but he doesn't quite understand it. It is partly his fault that Rose was corrupted by The Noble Circle of Horrorterrors and influenced by Doc Scratch, since he should've made her finish the main quest but didn't want to, since he was actually Rose's cat and didn't like his position as her supervisor.
Rose releases Jaspersprite from his job as her guide, giving him her laptop. Nepeta seems to have pestered him a few times, due to her love of cats and how Jaspers reminds her of Pounce de Leon. It was during one of these conversations that Jaspersprite revealed where he had been after he disappeared from Rose's house, though only identifying Roxy as another female human. Also in this conversation, he told Nepeta that since he got to be with Rose again after death, perhaps Nepeta will get to be with Karkat after hers. This eventually happens, in a dream bubble.
When Jade Harley went God Tier, she shrunk down LOLAR, with Jaspersprite still on it. She took LOLAR along with the other Lands and the Battlefield with her on her voyage through the Fourth Wall. Jaspersprite was later re-enlarged by Jade with a few other inhabitants of the Lands and the Battlefield as company for the duration of the trip across the Yellow Yard. He is seen aboard the ship here. One year into the trip, Jaspers brings John Egbert a cake that Nanna baked for his birthday and MEOWs the birthday song, causing Jade's dog instincts to kick in. An angered Jade chases Jaspersprite through a wall, slamming John against a wall in the process, causing him to black out.
Trivia
When John first observes Sassacre's daunting text, he notes that it would be heavy enough to kill a cat if dropped.
Frigglish, the character Roxy renames Jaspers after, was crushed by a giant book, providing more foreshadowing for Jaspers' eventual death.
Jaspers/Frigglish appears to have a dream self that is fully awake on Derse when Roxy began sleepwalking.