Fantastic Beasts 2: 10 Biggest Changes To Harry Potter Canon (And If They Work)

2. Dumbledore & Grindelwald's Blood Oath

The Change:

While we know that Dumbledore didn't move against Grindelwald until 1945, when the public outcry became so great and the danger so bad he had no choice, but this now explains why: the pair made a blood pact with one another, meaning that they literally cannot fight against each other. This also means that, despite Grindelwald fleeing after Ariana's death, this moment either had to come after she died (their fighting leads to it) but before he goes, further complicating their relationship, or it's the actual reason the spell deflected and killed her.

Does It Work?

Absolutely. This is the strongest change - or rather, addition - to the movie, because it underpins everything we know of what happened and actively strengthens it too. You can just about buy Dumbledore waiting until 1945 because of his love for Grindelwald, but it adds a massive layer of selfishness that doesn't fit. Having him magically unable keeps their relationship, but also fully explains why it took so long, as presumably it's not until then he figures out how to break it. If it's before Ariana's death, then it's an explanation that works better than it just being a stray spell, but making the pact after Ariana's death is fascinating too. It doubles down on the fact Albus knows in his heart that it was he responsible for killing his sister, and shows just how much love they still had for each other despite her death.