Now, not all inhabitants of Duckburg is as lucky as Gladstone is, Donald being one example. As there is so much information about witches, I have made a separate page on that topic, but there are things like curses, things that bring bad luck and demons.

Curses

On the third Wednesday after red Monday, everybody except Scrooge runs away from Duckburg. On that day all hair falls out. The ducks only gets slightly dizzy. Scrooge claims that an old totempole brought to Duckburg by Scrooge in 1908 is the cause of all that happens on Black Wednesday. Scrooge had sold the Chillyboot Indians some hair tonic which made them loose their hair. Blubber Face, their medicine man put a curse on that day: "Every year onum this Wednesday the hair of every crature nearum that totem pole shall fallum out!" Donald, Huey, Dewey and Louie goes to the Chillyboot Indians to sort things out in "Black Wednesday" (WDC 230-01). At the end of the story we learn that mould fumes from Scrooges money was the cause of Black Wednesday, not black magic. The "curse" proves to be superstition.
Voodoo, however, is not superstition. Scrooge once dispelled an African tribe from their land. Barks tells us about this in Voodoo Hoodoo (OS 238-02), and Don Rosa gives us some more information about what happened in part twelve of "The Life and Times of Scrooge McDuck" (The Empire-Builder from Calisota, (D 93288). A curse is put on Scrooge, and a zombie goes looking for him with a doll to squeeze. Donald and the boys later meet a man who has squeezed such a doll - he is shrunk. The voodoo magic works.

Things that bring bad luck

Scrooge loves collecting things, but sometimes he gets his hands on something that should have been sent to Farbackistan or Brutopia because they bring bad luck. In one story, "The Doom Diamond" (US 70-02), the ducks are exposed to Beagle attack, a live volcano and a stroke of lightening because Scrooge has bought the infamous Zero Diamond. The diamond had been put in a temple with scary statues outside to prevent accidents. At first, Scrooge does not believe that a diamond can bring bad luck, but towards the end of the story he has to admit that the Zero Diamond really does cause accidents and bad luck.
We see a similar case in Don Rosa's "The Curse of Nostrildamus" (AR 143), in which scrooge gets hold of an medallion which makes it possible to foresee the future. Scrooge wants to use it to foresee "every rise and fall of the stock market." The only thing Scrooge foresees, is what accident will happen five seconds into the future (Donald does not, poor fellow). The curse can only be lifted if Scrooge put the medallion back into the tomb.

I reckon that Scrooge is now convinced that things really can bring bad luck just as Donald may believe this after the affair with "The Mummy's Ring" (OS 29-01). Donald is given a stolen ring. Accidents has happened to the thief ever since he stole it. The ring brings Donald and the boys to Egypt, where they meet a cult worshipping the traditional Egyptian gods. All ends well for the ducks, but not for the thief - it brings bad luck to whoever steels it.