Fantastic Beasts 2: 10 Biggest Changes To Harry Potter Canon (And If They Work)
6. The Mirror Of Erised Basically Shows Flashbacks
The Change:
As we learned in The Philosopher's Stone, the Mirror of Erised shows us nothing but our heart's deepest desire. Which in this movie means... Dumbledore and Grindelwald making their blood oath, and then an appearance from Grindelwald as he appears now. There are ways you can argue this fits, but it makes the Mirror - which is at Hogwarts, despite supposedly being moved there to guard the stone - act more like a Pensieve.
Does It Work?
Only at a stretch. You can say that it fits with the established workings of the mirror because it shows him at the closest moment with the one person who truly understood him, which would be great, but then the scene doesn't really convey that - and that appearance of an older Grindelwald doesn't fit either. We also know that Dumbledore's Mirror vision later in life was Ariana and his family, but at this point it's still Grindelwald, even though he's actively trying to bring him down at the same time. There's something powerful in the reading of it being that first reading of their relationship, but at best the movie leaves it completely up to interpretation, and at worst makes it more like a flashback device.