Agatha Christie's 1939 AND THEN THERE WERE NONE novel is one of the best known works in which a group of victims are killed off serially in very "artful" ways, in this case in tune with an altered nursery-rhyme.
There had been many stories of bizarre killings in fiction and film up to that point, of course. But how many have this kind of "artful" attitude toward them, crafting a different approach to each victim?
I think most of the Holmes stories, when they do feature serial deaths, use the same method each time: attacking victims with a giant hound, or poison darts, or suchlike. The first version of the Joker only killed with his "Joker venom," though if I look around I can probably find him getting more creative over the years.
Armchair Appreciators of Artful Assassinations Assemble!