As a robot, BMO's gender alternates depending on who is speaking or what make-believe scenario BMO is playing out. Other characters will frequently refer to BMO using pronouns belonging to both genders. For instance, in "Conquest of Cuteness" Finn calls BMO "M'lady." In "Rainy Day Daydream," he refers to BMO using "he." In "Guardians of Sunshine," Sleepy Sam uses "he" when talking about BMO. Jake has also called BMO a "he" in "Return to the Nightosphere."
BMO will sometimes play pretend games in which it assumes a gender-specific role, such as calling itself a "little living boy" in "Five Short Graybles" and having its mirrored persona, Football, claim that it was "a real baby girl" in "Five More Short Graybles." Throughout the episode "BMO Noire" BMO role-plays as a hard-boiled, male detective; though it is to note the title of the episode treats "BMO" as a feminine noun by using "noire" instead of "noir."
In "Fionna and Cake," BMO is briefly seen in the tree house with no noticeable differences in design (aside from its controller), as opposed to the other characters who have all been gender-swapped, thus supporting that BMO has no gender.
In "James Baxter the Horse," BMO sings "BMO's Pregnant Song," which supports the idea that BMO is a female. However, it is fair to say that BMO is neither unambiguously male nor unambiguously female.
Football is the name used by BMO when talking to itself in the mirror. During this scene, BMO is a "little living boy" while Football is a robot as seen in "Five Short Graybles." BMO purposefully only plays with Football when Finn and Jake are not around. In "Five More Short Graybles," Football claims to be a "real baby girl," and BMO tries to teach Football manners.
BMO looks like a half-Macintosh half-Game Boy Color with Atari 2600 controllers. It also shares some traits with a Vectrex.
BMO is a medium-sized blue-green handheld gaming device, sometimes appearing with one or two controllers attached to it. When it is not being played it has an 8-bit face.
BMO's front includes an arrow pad, a floppy disk slot, multiple different shape buttons, two controller sockets, and of course the face, or screen. There is also a compartment with a red button hidden underneath the yellow D-pad.
On BMO's sides, the letters "BMO" are printed, indicating its name. BMO's arms emerge from the "O." There are also what appear to be holes for speakers at the tops of its sides.
BMO's back contains a battery compartment which holds 2 AA batteries, first seen in "BMO Lost." Normally the battery door is shown attached with 4 screws, however in "BMO Lost" it is shown with a tab at the top instead. There is also a slot which can be used for playing video tapes as seen in Holly Jolly Secrets Part I
BMO's default controllers highly resemble the Atari 2600 game console controllers, as they both only have a joystick and one red button. BMO's controller in "Too Young" slightly resembles a Sega Genesis controller for its button layout and handling design. An interesting note about this is that an Atari 2600 and a Sega Genesis controller have the same controller input device in reality, meaning that both controllers can be hooked up to the same device without issue.
BMO is sometimes seen with two slots to plug in controllers and sometimes with a compartment on that spot that opens up to where controllers can be plugged in.
Inside BMO is a gold heart with a face, as shown in "Be More." Pinned to the heart is a gold medal. Next to the heart is a small scroll tied with a red ribbon. This is a likely reference to the gifts given to the Scarecrow, Tin Woodsman and Cowardly Lion in the 1939 film The Wizard of Oz, symbolizing brains, courage and heart.
According to Finn, "BMO does weird junk when no one is around;" which he proved in "Five Short Graybles" where BMO talked to a mirror reflection named Football and pretended to be a "little living boy." In "BMO Noire," BMO acts out a film noir fantasy complete with giving names, voices and dialogue to a number of animals, and one inanimate object, in the house. The way it interacts with its reflection in "Five Short Graybles," as well as the animals in "BMO Noire," is evidence that BMO may suffer from dissociative identity disorder, otherwise known as multiple personality disorder. This causes BMO to act like completely different people, and have them communicate with each other.
BMO claims to not have emotions, but this is not true. In "Donny" BMO says, "I am incapable of emotion, but you are making me chafed!" It got annoyed in "Too Young" when Jake used BMO as an ottoman. BMO acted independently in "Slow Love" when BMO refused to turn down its music after Jake tells it to. Though they are both robots, BMO refuses Neptr's request to hang out more in "BMO Noire" by saying, "No, Neptr, I am not like you." In "Davey" BMO cries while Finn shaves his head to disguise as Davey. In the "Little Did You Know" DVD set, BMO's profile states that "he" is a good listener. In "James Baxter the Horse," its screen shows it crying and happy when James Baxter enters the scene.
BMO is very protective of Finn and Jake. In "Incendium" BMO said, "If anyone tries to hurt Finn, I will kill them," and in "Guardians of Sunshine" BMO refused to let Finn and Jake enter the video game world saying, "No! It's a far too dangerous, incredible adventure for you! That's final!"
BMO acts to keep the harmony of friendship between Finn and Jake. In "Video Makers" it edits the film Finn and Jake make in a way to resolve their dispute over artistic direction, even composing a song. In "Card Wars" it refuses to "play such games with Jake," because Jake cannot handle losing. When Finn asked for advice on Jake's attitude, BMO recommended that Finn play to lose.
BMO likes a number of games and even a few sports. BMO has been seen playing its video games by itself in "BMO Noire." BMO also has been seen skateboarding in "Card Wars" and in "Time Sandwich" and once had to be picked up from soccer in the episode "In Your Footsteps."
BMO likes scrambled eggs, as shown in "Her Parents," and hot chocolate, as shown in "Video Makers" and "Holly Jolly Secrets Part II," In "Five More Short Graybles," BMO was teaching Football manners. BMO drank the tea with its pinkie finger up but Football did not. BMO drank again and again and began to electrocute itself. This shows that even though BMO cannot drink things, it still does while pretending to be real. It has never been seen actually consuming food. It can cook, however, and made dinner for Finn and Jake in "Little Dude." BMO reveals in "The Creeps" that it enjoys taking nice pictures. BMO also likes to dance.
BMO is ticklish. This is shown when it giggles after Princess Bubblegum plays its circuits like a keyboard in "What Was Missing," when it reacts to being tickled by a feather in its sleep in "Guardians of Sunshine" and when it laughs and wriggles as its foot is being nibbled by a bear in "In Your Footsteps."
BMO's most prized possession is its controller, as it was stolen by the Door Lord in "What Was Missing."
In Adventure TimeEdit
BMO makes a cameo in the episode "Evicted!" being played by Marceline while Finn and Jake are house-hunting. In "Business Time," Finn and Jake play Adventure Master and Pro Football 1861 on it. It is later seen in the episode "My Two Favorite People." In "The Witch's Garden," Finn plays a game as he asks Jake how he got his magical powers. BMO also appears in "What is Life?" when Jake throws a garbage bag of butter on Finn, and in the episode "Donny," one of its controllers is smashed in half. BMO claims to not have emotions, but Donny angers it by breaking a controller and throwing it at BMO. In "Rainy Day Daydream," it shows a bored Finn and Jake a new game, "Conversation Parade."
BMO appears again in "Slow Love" where it acts like a rebellious kid, refusing to turn down its music when Jake tells it. BMO is then hit with a newspaper and told to have a timeout at a corner. BMO was then pummeled and battered when Snorlock started dancing with lady snails while the tree house was on its back, but was apparently unharmed and returned to play music at the end of the episode when Snorlock was kissing his new girlfriend.
In "Power Animal," BMO unintentionally distracted Jake with songs. They were later eating lunch together and Jake told BMO to hold his sandwich. BMO later fixes the well overhang that leads to the gnome's underground hideout that Jake had demolished while entering.
In "Guardians of Sunshine," it is revealed BMO has a button hidden under its control pad that allows people to be transported into one of its games. However, it does not allow Finn and Jake inside it, claiming it is too dangerous of an adventure. Despite its warning, Finn and Jake trick BMO by tickling it with a feather until it presses its button while it is sleeping. BMO later appears when Finn and Jake exit the game. While trying to tear a bomba out of the game's interface, they make a hole in it. BMO is then attacked by Sleepy Sam, Hunny Bunny, and Bouncy Bee for imprisoning them in the game. After Finn performs a combo move and destroys the monsters, BMO scolds them for going into the game and starts doing the combo move on them.
In "Video Makers," BMO serves as Finn and Jake's cameraman, filming random pieces of footage around the Land of Ooo with a video camera attached to its head at Finn and Jake's request, before they decide to make a real movie and argue about what kind of movie it will be. BMO, as their cameraman, witnesses their arguments, and instead of using the footage they captured for the movie, it makes its own animation while singing a song about how Finn and Jake should forget their argument and make up. At the end of the episode, BMO says Jake's favorite line throughout the episode, "Check, please!"
In the episode "Conquest of Cuteness," Finn and Jake call BMO over to get a camera to take pictures of the Cuties, but it turns out BMO is a camera, even though in the episode "Video Makers," BMO has a video camera strapped to its head. It is possible, however, that BMO's built-in camera only takes pictures.
In the episode "Too Young," BMO asks about Finn's date with Princess Bubblegum and does not tell Jake where the key is to the Wizard Tower in the video game. When Jake is trying to cheer Finn up when Princess Bubblegum jokingly "dumped" him, Jake puts both of his feet on BMO, using it as an ottoman, which annoys BMO.
BMO makes an appearance in "Fionna and Cake" in the opening and is later seen being played by Cake. Its appearance remains the same, supporting that it has no gender.
In the episode "What Was Missing," BMO has its controller stolen by the Door Lord and serves as a musical instrument during "I'm Just Your Problem." Marceline also used it to power a stove, showing that it is also a portable electrical outlet.
In the episode "The Creeps," it was in the mystery party when Finn and Jake came in the house. Its mystery name was Professor Pants. After the light went down and returned, BMO and Jake went to the basement to get some candles, but BMO was "killed" by the "ghost." At the end of the episode, it is discovered by Finn in Lady Rainicorn's body, being in the prank with Jake and the others.
BMO appears in "Incendium" watching over Finn while Jake was looking for another love interest for Finn.
BMO reappears in "Five Short Graybles" under the "Sight" segment of the episode (see article subsection "Football" below for more info).
BMO makes another appearance in "Beyond this Earthly Realm" when it amuses Finn with its fart noises. It also plays Finn's favorite song, "Three Baby Spiders"; a seeming nursery rhyme, BMO plays the song in a futile attempt to bring Finn back from the Spirit World.
In "Card Wars," BMO warns Finn about Jake taking the game too seriously.
BMO makes an appearance in "Burning Low." First, it tells Jake that he is late for a video chat with President Porpoise, and later on Jake plays an unknown game involving a rectangle punching, kicking, and jumping.
In "BMO Noire," BMO goes undercover as a detective to search for Finn's missing sock. The episode is narrated by BMO and is in black and white, similar to a 1940s- and '50s-era crime film. This is BMO's first central role.
BMO appears in "James Baxter the Horse" singing "BMO's Pregnant Song" and helps Finn and Jake create their routine.
BMO is once again the central character in "BMO Lost," where it is abducted by an eagle and has to find its way home through a forest. During its adventure, it meets Bubble and the baby Sparkle, whom it tries to help. Bubble ends up proposing to BMO but is popped by Jake.
In "Be More," BMO's purpose as "being more" is revealed, and it reunites with its father, Moe. BMO deletes some of its files for fun, but accidentally deletes its core system drivers. Finn and Jake discover where it was created when BMO tells them that it needs new drivers. When Moe tells Finn and Jake BMO's story, CMO approaches and gives the core system to Moe, who repairs BMO without erasing its memory.
On Sora's TeamEdit
When Finn and his friends joined the team, BMO became one of the guards to protect not only Finn and Jake, but mostly everyone.