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.
Like several other dog characters, Greater Dog becomes overexcited from physical attention. It is capable of extending its tail at a seemingly limitless rate when stimulated by being pet.
Greater Dog appears to enjoy spending its time off sentry duty by playing card games (namely, poker and go fish) against itself at Muffet's
- A dog resembling the Annoying Dog appears to the right of the screen and runs on the spot for a moment before leaping to where the protagonist's SOUL is. If the dog did not jump far, it is possible for the dog to start to jump as the attack ends.
- A blue spear comes in from the right of the screen and moves all the way to the left, followed by a white spear coming in from the left, stopping in the middle and moving back leftwards for a moment before the attack ends.
- Greater Dog will cease attacking once pet six times ("Critical pet!").
Greater Dog upon being pet enough times It is very easy to spare Greater Dog.
- If you pet Greater Dog once, you can spare it. If you keep petting it, its tail will keep rising, eventually ceasing its attacks, surpass the dialogue box, and even the menu. Greater Dog can be pet 54 times before petting it will not trigger new messages.
- Like other dog enemies, the Stick can be used to end the Greater Dog battle instantly.
- The Greater Dog's continuously rising tail may be a reference to the Long Cat internet meme.
- Greater Dog's name derives from the constellation Canis Major, which is Latin for "greater dog."
- The Red Bird NPC in Muffet's will comment on the disappearance of the Dogs, even if Greater Dog is still alive.
- Interestingly, Greater< Dog is never mentioned by the other guard dogs. Killing it provokes no reaction from the other dogs at Muffet's. In turn, if Greater Dog is the only guard dog left, how it acts at Muffet's does not change.
- If Greater Dog is the only enemy that you have killed, Alphys will comment on it, claiming that it was only seeking affection.
- The encounter of Greater Dog is completely random, like normal enemy encounters. It is always killed on a Genocide Route, though it is possible to move through Snowdin on a Neutral or True Pacifist Route without encountering it.
- However, if the protagonist never encounters Greater Dog on the Genocide route before facing The Gauntlet of Deadly Terror, Greater Dog is seen building snowdog. Also, the protagonist can find Greater Dog at Muffet's.
- Greater Dog's guard post contains a box of pomeraisins, and its weapon is made of pomer-granite. The joke here is a reference to the breed of dogs known as Pomeranian.