How Fantastic Beasts 2's Retcon Works
This is an interesting theory, and it fits with almost all the details shown in the Fantastic Beasts 2 trailers. It neatly explains the Elder Wand's absence in the first film and fixes the problem regarding Tina technically needing to be its master. It is important to note that this is a retcon, of course; there's no hint of it in the original books, which strongly implied Grindelwald acquired the Elder Wand shortly after he parted ways with Dumbledore.
So how does this theory explain Gregorovitch's brief glimpse of a youth? It's important to remember that Grindelwald is a master of disguise, as seen in Fantastic Beasts and Where to Find Them. He's aware of the history of the Elder Wand, and he knows that whoever owns it becomes a target. It would hardly be a surprise for Gellert to throw his potential challengers off the scent by disguising himself, and allowing Gregorovitch to catch a glimpse of a young thief. Where magic is involved, after all, it's not wise to believe your eyes. Jamie Campbell Bower played the part of young Grindelwald in a brief flashback scene in Harry Potter and the Deathly Hallows, a role he's reprising that role in Fantastic Beasts 2; this would provide the necessary parts to present this retcon in the movie.
It's worth noting that this doesn't explain the significance of Credence, nor does it provide a reason for Grindelwald's apparent interest in teaming up with an Obscurus. But any film has multiple layers of plot; Credence could easily be a secondary layer in this story, with the acquisition of the Elder Wand as the primary, driving narrative.
Is The Elder Wand More Important?
If the Elder Wand really is the MacGuffin of Fantastic Beasts: The Crimes of Grindelwald, then it raises an interesting question; is the Elder Wand even more important than we knew? There are two pieces of evidence that suggest it may well be. The first is the fact that, even armed with a normal wand, Grindelwald was a powerful enough sorcerer to take on the combined might of MACUSA's agents. He was only defeated in Fantastic Beasts and Where to Find Them because he encountered something he'd never expected in one of Newt's creatures. It's clear that, even without the Elder Wand, Grindelwald is a terrifying force to be reckoned with. How powerful would he be bearing the fabled Deathstick?
The second important clue is found in the history of the Elder Wand, in the tale of Godelot, who's mentioned in both Harry Potter and the Deathly Hallows and Rowling's tie-off book The Tales of Beedle the Bard. Godelot considered the Elder Wand itself to be his teacher. He described it as "My moste wicked and subtle friend, with bodie of Ellhorn, who knowes ways of magick most evil." It's already been established that wands retain a sort of "memory" of the spells that have been performed with them (that's the reason for the Priori Incantatem effect in Harry Potter and the Goblet of Fire). It seems that Godelot was able to use the Elder Wand to learn dark enchantments that would otherwise have been lost in the mists of time. What secrets of dark magic could Grindelwald gain from it? What long-forgotten enchantments could he master? Through the Elder Wand, some of the most powerful, brutal wizards in history would essentially become Grindelwald's mentors, and he would become a greater threat than ever before.
Where Voldemort only held the Elder Wand for a short period of time, and was never truly its master, Grindelwald won't lose the Deathstick until he's defeated by Dumbledore in 1945. That means he has years to train under the Elder Wand's tutelage, years to master the Dark Arts in ways nobody else has done before. Little wonder he becomes one of history's most dangerous sorcerers.
- Fantastic Beasts: The Crimes of Grindelwald/Fantastic Beasts 2 (2018) release date: Nov 16, 2018