These examples illustrate how sometimes seemingly innocent Halloween pranks aren’t so harmless.

The Minneapolis Journal 2 Nov. 1904

Rosa Hager of Cleveland was the target of a Halloween prank in 1904 while alone in the house of her employer. Details of the prank aren’t clear, but the article suggests that someone dressed as a monster or a devil frightened her so badly that she had to be taken to the jail as a “raving maniac.” Rosa claimed that the devil appeared to her because she’d visited a fortune teller and feared it would eventually return to kill her.

The Free Lance [Fredericksburg, VA] 2 Nov. 1907

In 1907 14-year-old Joseph Barbenero pretended to rescue a girl from his 12-year-old friend Frank Reynolds when he shot him through the head with a “harmless pistol.”

Margaret Dissett, a Buffalo teenager, was fatally burned while burning a bowl of wood alcohol.

I located the text of another more detailed blurb about Margaret’s death.
Margaret, the 15 year old daughter of Capt. John Dissett died at the family home, 381 Fargo Ave. at 8 o’clock this morning from the effects of burns she sustained by an explosion last night. Her entire body was seared by the flames and her suffering until death came was terrible. Miss Dissett gave a Halloween party at her home last night. A game started which required the use of burning wood alcohol in a tin pan. The flames burned low in the receptacle and the girl poured a fresh supply into the pan. There was an explosion and Miss Dissett’s clothing ignited. Before those present could aid her, she was a sheet of flames. A young man named Ronan pulled off his coat and wrapped it about her, smothering the flames.” (-The Evening News, N. Tonawanda, Friday, Nov. 1, 1907)

The Palestine Daily Herald [TX] 1 Nov. 1907

Also on Halloween 1907, someone knocked on the door of the Stiver home in Logansport, Indiana. When the daughter opened the door, the prankster thrust a pumpkin head into her face. Her mother, Sadie Stiver, heard her daughter’s screams and “dropped dead from heart failure.”

The Paducah Sun [KY] 3 Nov. 1903
This is another story involving careless gun-handling at a Halloween event. Twenty-year-old Horace Benton, under the impression that his pistol was loaded with blanks, accidentally shot and killed his friend Josiah Sutton.
The Spanish Fork Press [UT] 7 Nov. 1907
Ramon Lavota and his friends thought it would be amusing to trip someone by secretly holding a wire across a sidewalk. The joke worked but the victim of the prank pulled a firearm and fatally shot Lavota.
The North Platte Semi-Weekly Tribune 17 Nov. 1908

Nicholas Offutt, his younger sister, and several other costumed youths entered Frank Kretzmer’s store on Halloween and “played childish pranks.” According to this blurb, Kretzmer removed Offutt’s sister’s mask, an act which resulted in a fatal affray.