A crystal ball is a device commonly used by fortune tellers to see into the spirit realm so that they can see into the future. It also had other uses depending on its creator and who was using it.
In the 1980s cartoon show version of "The Astro Smurf", Gargamel created a crystal ball he could use to track down the Smurfs. However, it led him to the mountain where, instead of finding Smurfs, he found their disguised form of Swoofs as they were busy making Dreamy believe that his birthday wish of traveling to the stars has come true. Papa Smurf, noticing that Gargamel was nearby, had sent him away by creating a localized thundercloud that followed him around, with the initial lightning bolt from it making Gargamel lose his crystal ball as it shattered on the rocks.
In "Now You Smurf 'Em, Now You Don't", the trolls used a crystal ball that allowed Smurfs to see their fondest dreams in it, with the catch that it would transport whoever touched the crystal ball into their underground lair where they would be put to work. Papa Smurf, however, found out that he could send sunlight down into the tunnels to blind the trolls through the crystal ball. As the main crystal ball that the trolls owned was shattered, rendering the one that the Smurfs owned useless, they decided to put it to better use by turning it into a bowling ball.
In "Gargamel's Miss-Fortune", Esmeralda Fortune uses her crystal ball to trick people into thinking she can see into the spirit realm, and had Papa Smurf hide inside her crystal ball to make it appear that Gargamel was now seeing a vision of him from the future telling the evil wizard that he would be haunted by Smurfs forever.
In the 2021 cartoon show episode "Clumsy Not Clumsy", Gargamel uses a crystal ball to help him find his way to the Smurf Village after purposely letting Clumsy use the Opposite Amulet to escape.
Gargamel also uses a crystal ball in 2021's "The Smurfs Show" as a kind of television device with the help of which Gargamel can spy on the Smurfs through Baby's teddy bear's eye. He then watches different kinds of shows the Smurfs prepare for him and later they tell him about their trumped-up story through that crystal ball.