"Uh... Goodbye, Mushroom... You were such a good puppy. I'll always remember... running through the snow with you. And... how you'd snuggle... and... I'll never forget you... Never." — Daniel in Episode 2: Rules
Mushroom is an easily excitable and friendly dog. She appears to grow quickly attached to new people, given how she responds positively towards strangers petting her and how rapidly she becomes fond of Daniel after being taken in by him. She doesn't really listen to Sean and mostly only to Daniel, possibly because Daniel took her with him and spends time with her.
- "Let's see... How about... "Mushroom"? She totally looks like a mushroom!"
- — Daniel to Sean in "Roads"
Episode One - "Roads"
During their rest stop at Bear Station, Sean and Daniel come across a dog sleeping in a laundry basket behind the store's counter. After Daniel asks Sean whether they can adopt her, Doris Stamper informs the two that her owner needs to be an adult, which they reluctantly accept. Later on, after freeing Sean from the gas station's back office and incapacitating his captor, Hank Stamper, Daniel wraps the dog in her blanket and takes her with them off-screen, unbeknownst to Sean.
While in Brody's car, Sean hears a yap from the back seat and turns to discover Daniel hiding something beneath a blanket. After initially trying to pass it off as a cough, Daniel reveals that he took the dog from the gas station and attempts to convince Sean to let them keep her. After some reluctance, Sean gives in, and Daniel gives her the name "Mushroom". As Brody drives onward, Daniel falls asleep with Mushroom sleeping in his arms.
Later, while waiting for Brody outside of Three Seals Motel, Sean watches Daniel and Mushroom play before Sean decides to play fetch with her. Before leaving, Brody gives Daniel a red bandanna, which he decides to put on Mushroom. In the motel room, Daniel keeps Mushroom close to him while watching TV before taking her with him to have a bath. After discovering about his father's death via the news channel, Daniel causes a miniature storm in the room, causing Mushroom to hide under a desk and bark.
The following morning, Mushroom can be seen sleeping in Daniel's lap as they ride the bus.
Episode Two - "Rules"
As the episode begins, Mushroom is seen running through the snow as Sean trains Daniel to strengthen his telekinesis. While searching for objects to have him test his powers on, Sean can ask Daniel to lift Mushroom, to which Daniel refuses. Sean, Daniel, and Mushroom later enter the abandoned cabin they found to stay in temporarily. Mushroom promptly sits on the mattress with Daniel, and as he coughs, she lays her head down on his lap to comfort him.
The following day, as they are about to embark onto their journey towards their grandparents' house, Sean and Daniel suddenly notice that Mushroom is missing and begin to search around the area. After Sean finds Mushroom's bandanna lying in the snow and follows a trail of blood, he finds Daniel standing over Mushroom's dead body, having been killed by a wild cougar. Sean is given the choice either to let Daniel avenge Mushroom, resulting in him snapping the cougar's neck, killing it, or to interfere with Daniel, causing the cougar to flee the scene with Mushroom's body. Depending on this choice, the brothers either bury Mushroom or create an empty monument before they set off to their grandparent's house.
In Life is Strange games, the color red is strongly associated with death. Mushroom wears Brody's old red bandana and loses it after being killed.
- Mushroom's breed may be German Shorthaired Pointer.
- If Doris isn't wary towards Sean, she reveals to him and Daniel that Mushroom was abandoned on the side of the road.