For about a year now, Fantastic Beasts: The Crimes of Grindelwald has been using an image of the Elder Wand in promotional teases, as pointed out by The Ringer. You surely remember the instrument—which is said to be the most powerful wand to have ever existed in JK Rowling's Wizarding World—from the original Harry Potter series. So just how important will it be to the Fantastic Beasts sequel? Extremely.
According to Pottermore, the Elder Wand (also known as the Deathstick or "The Wand of Destiny") is the most sought after of the three Deathly Hallows. According to "The Tale of the Three Brothers," a fairy tale often told to wizard children, the Elder Wand was given to Antioch Peverell by Death himself. Whoever was able to reunite the wand with the other two Deathly Hallows—the Resurrection Stone and the Cloak of Invisibility—would become the Master of Death.
As such, the Elder Wand is extremely dangerous—and can be made even more so, depending on the intentions of the wizard who possesses it. As Dumbledore once said in The Tales of Beedle the Bard, "Those who are knowledgeable about wandlore will agree that wands do indeed absorb the expertise of those who use them."
So how does all of this connect to Fantastic Beasts? While in disguise in the first Fantastic Beasts movie, Gellert Grindelwald didn't carry the Elder Wand—though we know from previous installments that he had acquired it by the time the first movie takes place. Grindelwald stole the wand from Mykew Gregorovitch, stunning the wizard to gain the allegiance of the Elder Wand, sometime before 1926. But while promotional stills indicate that Grindelwald will have physical possession of the wand in this second movie, which witch or wizard has the wand's allegiance is less clear—after all, Newt Scamander captured Grindelwald at the end of the first film, and Tina Goldstein disarmed him.
However, we know from the Harry Potter series that Dumbledore takes possession of the Elder Wand after a duel in 1945, which is the same year the Fantastic Beasts series will end (so it's pretty safe to assume that Dumbledore and Grindelwald will face off in the series' fifth and final film). And Dumbledore's own words about how he came to possess the wand in Harry Potter and the Deathly Hallows are also particularly telling. "I was fit to own the Elder Wand, and not to boast of it, and not to kill with it," he stated in the novel. "I was permitted to tame and to use it, because I took it, not for gain, but to save others from it."
We'll have to wait until this weekend to see how it all plays out in The Crimes of Grindelwald, but this is one story that will take several more installments to tell.