Greater Dog's fur is wholly white, and it wears mantle-gray armor adorned at the wrists with apparently functional dog faces, much like the spear weapon it holds during battle. However, Greater Dog itself only fills the smallest neck portion and the tail area of the armor while controlling the rest of the suit through unknown means. Notably, when it jumps out of the suit, its "hands" seem to withdraw into the armor and don't reappear when it hops back in backwards.
Greater Dog is incredibly affectionate and constantly seeks attention; Dogamy even warns the protagonist of facing the full brunt of Greater Dog's playful attitude if they are not careful of where they sit down in Grillby's bar.
It sits with most of the other dog characters in Grillby's when it is not on sentry duty and appears to be unable to say much more than a sound effect while making a pleased expression (though this expression becomes a frown if both Doggo and the Dogi have been killed).
Greater Dog appears in the True Pacifist Route epilogue outside the Snowdin library with most of the other dog characters, playing happily with Endogeny, making its trademark facial expression and sound effect (which the Endogeny seems to now share).
A scene shown during the credits shows it hiding within a poff of sand on a beach with Undyne and Alphys, much like it did with the snow before battling it, while Lesser Dog performs a similarly familiar pastime nearby. Its yellow text in the credits also lists it as being excited by life's changes.
- Its dog-faced spear flies from the right of the screen to the left, flickering from blue to white at short intervals.
- An Annoying Dog-like canine lies at the bottom of the screen, first sleeping but quickly awakens and fires off the word "BARK" towards the SOUL as soon as you move. If the protagonist stays completely still once the turn starts, the dog continues to sleep through the turn without attacking.
- To spare it, the protagonist must beckon/ignore, then pet, then play, and then pet twice.
- Like any other dog enemy, it can be spared by using the Stick.
- Ignoring four times bores Greater Dog and ends the fight.
- It's so excited that it thinks fighting is just play. [Check]
- It's the Greater Dog. [Encounter]
- Greater Dog is seeking affection. [Neutral]
- Greater Dog is waiting for your command. [Neutral]
- Greater Dog is watching you intently. [Neutral]
- Greater Dog is too far away to pet. You just pet the air. [Pet]
- Greater Dog is not excited enough to play with. [Play]
- You call the Greater Dog. It bounds toward you, flecking slobber into your face. [Beckon]
- Greater Dog's ears perk up. Nothing else happens. [Beckon again]
- Greater Dog curls up in your lap as it is pet by you. It gets so comfortable it falls asleep... Zzzzz... ... Then it wakes up! It's so excited! [Pet after Beckon or Ignore]
- Greater Dog's excitement is creating a power field that prevents petting. [Pet again]
- You make a snowball and throw it for the dog to fetch. It splats on the ground. Greater Dog picks up all the snow in the area and brings it to you. Now dog is very tired... It rests its head on you... [Play after Pet]
- As you pet the dog, it sinks its entire weight into you... Your movements slow. But, you still haven't pet enough...! [Pet after Play]
- You pet decisively. Pet capacity reaches 100 percent. The dog flops over with its legs hanging in the air. [Pet #2 after Play]
- Tummy rubs are forbidden. [Pet again]
- Greater Dog is too tired to play. [Play again]
- Greater Dog inches closer. [Ignore]
- Greater Dog is making puppy-dog eyes. [Ignore 3 times]
- Greater Dog decides you are too boring. [Ignore 4+ times]
- Greater Dog is patting the ground with its front paws. [Neutral after petting]
- Greater Dog wants some TLC. [Neutral after playing]
- Pet capacity is 40-percent. [Neutral after petting again]
- Greater Dog just wants affection. [Neutral after ignoring]
- Greater Dog is contented. [Neutral after meeting spare conditions]
- You threw the stick and the dog ran to get it. You played fetch for a while. [Use Stick]
- Greater Dog is panting slowly. [Low HP]
- Greater Dog's name derives from the constellation "Canis Major," which is Latin for "greater dog."
- Greater Dog's sound effect sounds very similar to Wario's ground pound sound effect from Super Mario Land 2: 6 Golden Coins.
- Greater Dog is referred to with the pronoun "it" in battle; however, Doggo refers to Greater Dog using the pronoun "he" when spoken to in Grillby's if the Dogi have been killed.
- Papyrus also refers to Greater Dog using "he" if the protagonist calls him in the area they first met Greater Dog.