Uncle Arthur

Uncle Arthur - or simply known as Arthur - is a member of the family and a non-canon cartoon counterpart to Arthur, appearing in the Christmas Special "My Two Front Teeth".

Personality
From the animated short, Arthur seems quite cheery when arriving at the small cabin. Some might even compare him to Saint Nick himself. He's even generous to give Sofia a pencil with paper to write down her Christmas wish list, going so far as to help suggest a few things when she cannot think about what she wants.

Arthur also seems very generous in complimenting Gloria (Martin's wife) when discussing about her "famous cooking" with Sofia. And, when both Gloria and Martin "fall ill", he takes it upon himself to take for the children by baking some sweet treats with them.

Appearance
Uncle Arthur appears to be a well built man with ginger hair, a matching beard, green eyes and porcelain skin. His attire consists of a red checkered and buttoned up top, blue overalls, brown shoes and a traditional Christmas hat to accompany his look.

Story
Within the beginning of "My Two Front Teeth", Uncle Arthur appears at the door after Sofia answers, enthusiastically greeting her with a smile and her own Christmas wish list. When she's unsure of what she wants, he happily responds with "You could always ask for a bigger mouth like mine" that allows him to taste more of her mother's great cooking, prompting Sofia to ask Santa for her two front teeth when Arthur grins revealing a triumphant smile.

On the 22nd of December - a day has passed since the initial beginning - Arthur is found in the living-room after Sofia attempts to talk with Gloria only to receive silence in return during their encounter in the hallway. He then approaches her with a gift, informing her that it was made by Martin who told him that she couldn't open it until Christmas morning had arrived. He also mentions about the gift being particularly heavy.

The group decide that since Gloria and Martin are under the weather, they'll bake some cookies instead. Arthur makes a subtle reference to The Ice-Cream Man in this scene as he mentions to keeping them away from him due to the fact he "loves sweets".

As Arthur showcases the cookies to Sofia and Henry, each represent the family in this order: Henry, Sofia, Gloria?, Arthur and Martin. One cookie however seems horrifically burnt to a crisp, blackened and shriveled up. When Sofia comments about what happened to the cookie, Arthur briefly states "That one was imperfect-" before a jumpscare using the cartoon's introduction appears, ending the scene.

As the cartoon returns, the day ends like previously with Sofia complaining about how much she's eaten before being sent to bed in hopes of feeling better the next morning. This time it is by Arthur since Gloria is nowhere in sight. As Sofia and Henry rest, a pixelated version of Arthur's face centers the camera as a slightly muffled chuckle is heard and repeated. As the chuckle repeats itself for a second time, Arthur loses his eyes as tears of blood stream down his face. Another jumpscare will play out with a more distorted yet life-like version of Arthur staring at the camera with a flashing red tint whilst a song accompanies in the background. If you glance over to the right of the screen, another face can be seen abruptly before the scene ends.

To confirm his death off-screen, another snowman is placed alongside the other two, signifying that Arthur has unfortunately been killed off.

Trivia

 * Most of the deaths that occur take place off-screen, including Arthur's.
 * Despite this, there's no clear sign for how Arthur was killed off considering he was in the cabin with the children. It could be a possibility that Arthur had wanted to investigate what was happening to Martin and Gloria but was murdered in the process by them or the supposed demonic entity haunting the family.
 * Arthur's voice is heard calling out to Henry, leading to his death in the process. Whether or not this had been Arthur is unknown since there's been no indication as to what may have been present to mimic his voice.
 * Ironically enough, some fans have spotted that when Arthur suggests Sofia should ask for a bigger mouth like his, an image at the end of the cartoon reveals Sofia's deformation via having her mouth split from the middle and stretch downwards.