The owl first appears in "Prisoners of Love" in Ice King's Imagination Zone, after Ice King is knocked out by Finn. When Ice King contemplates why people do not like him, the Cosmic Owl answers, "You're a sociopath."
The Cosmic Owl again appears in the episode "Donny" as a drawing made by the Why-Wolf. It is stated that the Why-wolves, if not stopped, would ravage the world and overpopulate until the Cosmic Owl would be forced to intervene by devouring them all, as is the course of nature.
He appears in "The New Frontier" at the end of Jake's "croak dream," and Finn and Jake's later conversation suggests that it is well known that the Cosmic Owl is supposed to show up in croak dreams. The owl is also featured prominently on the episode's title card.
The Cosmic Owl also appears in "The Lich," where he is seen in Finn's dream on a television screen, indicating that Finn is in a "premonition dream."
He also appears in "Jake the Dog," visiting his friend Prismo in the Time Room inside the Multiverse while Jake is making his wish. At first, he is disappointed that he and Prismo could not play board games like they planned to, but he does join Jake and Prismo in the pool party.
In "Frost & Fire," the Cosmic Owl appears in Finn's dreams, foretelling his inevitable break-up with Flame Princess. Three times, Finn attempts to experience the "cool" and "important" dream again because the Cosmic Owl is there. Over the three dreams, the Cosmic Owl whispers something that Finn cannot hear, until the final premonition dream, where he stands directly in front of him. At this point, Flame Princess and Ice King are engaging in a full-out war. The Owl tells him knowingly, "You blew it." After Flame Princess breaks up with Finn, the premonition is realized, and Ice King repeats the Cosmic Owl's message to Finn: "You blew it, man."
The Cosmic Owl makes an appearance in "Wake Up," at Prismo's party. When Jake and Finn return to the Time Room, the Cosmic Owl is seen wanting to play another round of Card Wars with a disgruntled Prismo. He soon leaves after they begin talking about the Citadel.
The Cosmic Owl makes a starring role in "Hoots," which reveals that he crashes in a cosmic motel and plays board games when he's not out making croak dreams come true. He would later become infatuated with the dream version of Gunter, only to end their relationship after causing a premonition dream of Princess Bubblegum's foreshadowed usurpation in the Candy Kingdom.
In "Come Along With Me," wanting to stop the Gum War, Finn and Jake unleashed the nightmare juice given to them by Nightmare Princess, forcing them, Princess Bubblegum, Gumbald, and Fern into a hallucinatory slumber. At the beginning of the dream, a singing Poodle Woman appears.
Inside the dream realm, PB and Gumbald continue to be hostile towards each other and despite Finn's protests, PB decides to pursue Gumbald. Finn attempts to appeal to Fern by reminding him that they are "two sides of the same coin" and that they share the same torment. PB and Gumbald recreate a nightmare version of the moment that PB defeated Gumbald by dousing him with his own dum-dum juice, only this time with the roles reversed. PB is doused and is transformed into a smaller, less intelligent version of herself. PB and Gumbald are later brought to tears after both witnessed the Candy Kingdom turn into a pile of goo.
Finn and Fern continue fighting but are able to find common ground after Jake brings them Finn's vault. Together, they dive in and confront the Grass Demon. Fern kills it, ridding himself of its influence once and for all. Just after, the Poodle Woman flies by who is revealed to be the Cosmic Owl in disguise, thus making the dream a premonition. The dream came true, as with no Grass Demon to control him, Fern begins to deteriorate in the real world.
- "Prisoners of Love" (debut)
- "Donny" (as a drawing)
- "The New Frontier"
- "The Lich"
- "Wake Up"
- "Skyhooks II" (cameo)
- "Come Along With Me" (cameo)
You're a sociopath.
Hello, Hello! Hey so I brought over the- (gasps) What is this singular doing in this realm?!
But I brought games! We were gonna hang...
Ok. (flies over and lands in the Hot tub)
You (talking to Finn) blew it.
- The Cosmic Owl's design is based on the reflection of light off a urinal at Cartoon Network Studios.
- On a similar note, his design may have contributed to the Solar Owl pet design in Realm Of The Mad God
- The Cosmic Owl may also be a psychopomp who guides souls to the Land of the Dead, since he is so important in croak dreams.
- In "Prisoners of Love," "Jake the Dog," "Frost & Fire," and "Wake Up," he actually speaks with real words instead of making bird noises.
- The Cosmic Owl is shown to be friends with Prismo.
- The episode "Jake the Dog" is the first physical appearance of the Cosmic Owl, and not a dream.
- His color is in a lighter shade of yellow than his previous appearances.
- Adam Muto has confirmed that the Cosmic Owl has some role of importance in Ooo.
- The Cosmic Owl's ability to cause premonition dreams was explained in "Hoots." It is shown that, while it is a duty of his to cause specific dreams to come true, any dream he enters will come true because of his presence alone.
- Finn decided not to listen to him anymore because he blames Cosmic Owl for his break-up with Flame Princess as revealed in "Hoots."