Harry Potter: 15 WORST Plot-Holes In Wizarding World Movies

13. The Blood Oath

The introduction of the blood oath between Dumbledore and Grindelwald in the Fantastic Beasts sequel is a great way of making Dumbledore's reluctance to fight his former friend (and possible lover) only about residual feelings for him. It added a little more logic, establishing that the oath strictly forebade Albus taking up arms against the dark wizard.

But, when exactly did they take the oath together? The fact is, because of the three-way duel between the pair and Aberforth that led to the death of Ariana Dumbledore, the oath has to have been made after Ariana's death. Otherwise they could never have fought in the first place. However, after the duel, they weren't exactly on speaking terms, since Ariana was dead and Grindelwald immediately fled the country.

Also, the books establish that Albus and Grindelwald didn't see each other for decades after their duel (until they faced one another again), so there is literally no time for that to have happened.

Additionally, the Mirror Of Erised shows you your greatest desires, it doesn't show you a memory of the past, so how could Dumbledore use it like that? As if it was a pensive?!