The tone is self-pitying "It was bad enough having an invalid brother, but having one who possibly was not all there was unbearable, so I began to make plans to kill him by smothering him with a pillow." Instead of feeling bad for his brother who is suffering from a deadly illness he pitties himself because his brother in "invalid".
The word choice in the story leads to foreshadowing. Throughout the story the older brother uses words such as he was implying that the brother was no longer with him. This foreshadowed him either passing away or on of the brothers moving.
In the story the older brother uses imagery to describe the scene of where he is trying to teach his younger brother to walk. "We were down in Old Woman Swamp and it was spring and the sick-sweet smell of bay flowers hung everywhere like a mournful song."
The style is mournful. The older brother says things such as "But sometimes, as I sit in the cool, green-draped parlor, the grindstone begins to turn, and time with all its changes is ground away-and I remember Doodle."
The theme is constant rudeness to Doodle. The family made him a coffin before he died, also when his brother makes him touch the coffin and when his brother leaves him in the storm out of spite.