Mouse seems to possess an extremely high intelligence, able to formulate complex plans and understand instructions. He is a capable fighter and fast runner, and in combat will occasionally emit a nimbus of pale blue light. His bark is capable of breaking people out of an enchanted sleep, and spur them to action. He also seems to possess an endurance and healing ability far beyond mortal dogs; a few hours after being hit by a car, he can fight a White Court vampire and his henchman.
Mouse likes going places in the Blue Beetle, he is large enough so that he filled up most of the back seat. It does not matter that they are headed into danger; for Mouse it is all about the journey, not the destination. He also makes sure he has his own lead when he goes out with Dresden or Molly. Dresden suspects this is to make people feel more comfortable around a big dog safely tethered; he's a people canine.
Mouse is one of a group of Temple Dogs puppies believed to have Foo Dog ancestry, found and rescued by Harry Dresden after he was hired by the Tibetan monk, Brother Wang. The puppies are returned to the monk, but Mouse hides in Dresden's car, the Blue Beetle, missing the flight back to Tibet, and remaining with Dresden during the events of Blood Rites. Dresden ultimately decides to keep the dog and names him Mouse.
In the seriesEdit
In White Night, when Anna Ash’s apartment building is on fire, and all of the residents were asleep because of a sleeping spell, the Ordo Lebes women were trapped in Anna’s apartment because a predator who had been stalking them is outside of her door laying in wait. Mouse lets out an extremely loud “WOOF” repeatedly and with mechanical regularity. The scale of it was similar to a Civil Defense storm warning. Dresden describes it like a flood of sound, a solid living cascade that rattles your brain. All of the residents awoke and vacated safely without panic. The Ordo were able to escape with the evacuation.
In "Dog Men", Mouse accompanies Harry Dresden and Joseph Listens-to-Wind to Taylor, MS. He is attacked by the local Wolf people, prompting Dresden and Listens-to-Wind's to fight against the wolf people. Later, he follows Dresden and Deputy Gentle to the morgue where he picks up a scent.
In Turn Coat, Mouse saves Molly Carpenter by putting himself between Molly and Morgan's bullet. She pulls it out, crying. As soon as Molly leaves the room, he is up and walking normally, having faked it to make Molly feel her error more. As a Foo Dog, he is strong, and probably didn't need the medical care. He saves her again when Samuel Peabody releases the Mistfiend at Morgan's trial when he's outed as the real murderer and the Council's traitor. 
Mouse also identifies Peabody as the the one who came through the Ways into Chicago. Ancient Mai declares Mouse a Foo Dog and therefore able to give testimony at Morgan's trial at White Council headquarters in Edinburgh, as did several of Aleron LaFortier's Asian supporters. Ancient Mai says, "Where did you get such a thing and why are you allowed to keep it?" To which Dresden replies, "He sort of picked me."
In Changes, a faint blue nimbus of light surrounds Mouse when he attacks the Ik'k'uox. The Ick threw Mouse by his tail, he hit the ground hard, letting our a cry of pain. Dresden blasted the Ick with Soulfire saying “get off my dog”.
Thomas Raith comes to after his encounter with the Ick, then Thomas and Mouse team up. Thomas tells Mouse, "this time we do it smart", he got its attention so that Mouse can get its hamstrings. Faint blue light surrounds Mouse again and they take off zero to cheetah in a second—Mouse lets out a battle roar. Mouse is referred to by the Red Court vampires, the Eebs, as a "Mountain Ice Demon from the Land of Dreams".
While Dresden's raiding party is transformed into hounds by Leanansidhe so that they can traverse the jungle to Chichen Itza more quickly, Mouse talks to them. He leads the pack saying, "Follow me." He later threatens to bite Lea's ass off if she doesn't change them back to humans. Acting indifferently, Lea, says that Mouse is far from his source of power, implying that he might not win such an engagement with her. Mouse replies, "I live with a wizard. I cheat."
In Ghost Story, Molly Carpenter informs Harry Dresden that "Chewbacca is with her" indicating that Mouse is with Maggie. Later, Uriel the archangel takes Dresden to the Carpenter home where Mouse lives with Maggie Dresden, referring to the dog as Little Brother and reassures Dresden that Temple Dogs have been known to live for centuries.
In Skin Game, Mouse is formally attached to Maggie as a medical assist dog in order to prevent any panic attack she may be subjected to; he's a favorite of other schoolchildren, a few of them being allowed to play with him.
He's at Maggie's side when she meets her father, providing both physical and emotional support, and she refers to him as the monster under her bed; both of them "slayerized" another monster that was there. Dresden worries he might get a better formal education than he can ever hope to earn.
Mouse joins the fight when Nicodemus Archleone's band attacks the Carpenter's home, standing beside a helpless, Grace-less Uriel. However, he takes a more active role in the fight at Waldo Butters' side when the latter wields Fidelacchius against Archleone.
In "Christmas Eve", Mouse helps Harry Dresden build a red bike for Dresden's daughter, Maggie, displayng a far greater mechanical talent than Dresden. During her visit to them, Mab politely greets him, calling him Guardian.
Word of JimEdit
[Mouse] does have a bunch of brothers and sisters who wonder how come they haven’t heard from him. ‘You never howl, you never pee on anything….’ And plus, there is…uh, I will just say that the possibility exists that Harry didn’t rescue all of them, and if so, where are the others?— Jim Butcher, noting that the evil sorcerer might still have one or more of Brother Wang’s puppies, leaving open a possible future meeting with Mouse’s "evil twin".Jim Butcher has stated that the breed that Mouse most closely resembles is the Caucasian Mountain Dog.[Footnote 1]
Jim has also noted that, though it may never come up in the series, Foo dogs traditionally draw their power from the threshold of their home, and that Mouse became much more powerful when he moved into the Carpenter household as a result. Mouse, he notes, had been forced to learn to draw from "other kinds of power" due in part both to Harry Dresden's tendency to flout convention and the comparatively weak threshold of Dresden's old apartment.
- ↑ Jim Butcher Tweet
- ↑ Jim Butcher Tweet
- ↑ 3.0 3.1 Proven Guilty, ch. 28
- ↑ White Night, ch. 25
- ↑ Dead Beat, ch. 3
- ↑ Changes, ch. 9
- ↑ Blood Rites, ch. 1 & 2
- ↑ Blood Rites, ch. 42
- ↑ Dead Beat, ch. 1
- ↑ Dead Beat, ch. 2
- ↑ White Night, ch. 12
- ↑ "Down Town"
- ↑ "Heorot"
- ↑ Small Favor, ch. 19
- ↑ "Wild Card"
- ↑ "Dog Men"
- ↑ Turn Coat, ch. 34
- ↑ 18.0 18.1 Turn Coat, ch. 47
- ↑ Changes, ch. 25
- ↑ Changes, ch. 41
- ↑ Ghost Story, ch. 11
- ↑ Ghost Story, ch. 50
- ↑ Skin Game, ch. 20
- ↑ Skin Game, ch. 32
- ↑ Skin Game, ch. 49
- ↑ Skin Game, ch. 51
- ↑ "Zoo Day"
- ↑ "Christmas Eve"
- ↑ 29.0 29.1 White Night, ch. 12
- ↑ 30.0 30.1 WoJ on Harry's Family
- ↑ Jim Butcher Reddit AMA