We get this ignorance every Halloween on here (largely as its predominantly English posters on here).
Halloween, as celebrated today, is a secular Irish/Scottish custom. All of it.
Minor details such as swapping a pumpkin (US) for a turnip (which I carved), and saying "trick or treat" (a phrase from Canada) rather than the numerous interjections that preceded it, are the only changes from the Halloween of my youth, and my parents, and their parents.
Guisers from 1890 in Ayr, Scotland;
"I had mind it was Halloween . . . the wee boys were at it already, running about with their false faces on and their bits o’ turnip lanterns in their hand."
*False faces is what we in Ireland (and Scotland) call masks.
Guising is then first recorded in North America in 1911 (Irish/Scottish migration), in Ontario, Canada, the same province where 6 years later today's most common interjection "trick or treat" was first used.
Back to The Irish Times (from 2014)
"The expression trick or treat has only been used at front doors for the last 10 to 15 years. Before that "Help the Halloween Party" seems to have been the most popular phrase to holler."
And regards pranks, ghosts etc, this has been recorded at Halloween here for over two centuries. Scottish poet John Mayne from 1780: "What fearfu' pranks ensue".