"Like it or not," said Grindelwald, "joining me is the only way you can save your lovely sweetheart. Albus Dumbledore is the only wizard who can beat me in combat, and he will not face me due to our ambiguous relationship."
"Ambiguous how?" asked Credence.
"I'd rather not say. This is the 1920s, after all."
"But it won't be a wizard you'll be facing," said Newt. With that, he opened his case and set loose his goriffalo, which was a cross between a gorilla and a buffalo. This brilliantly kept Newt's beasts vaguely relevant to the story.
"NOOOOOO!" cried Grindelwald, running away as the goriffalo charged him. All the Muggle bystanders, who couldn't see the goriffalo, laughed at the sight of this strange man running away from nothing.
By the way, it turns out Newt has a secret extra brother who has never been mentioned before. This is canon now.
"You may have beaten me this time," shouted Grindelwald, "but your silly Muggle friend is still mine!"
"Hey, that rhymed!" said Credence, although actually it didn't rhyme. "It could be a song!"
And then, Grindelwald Disapparated, but none of the Muggle bystanders noticed because they never notice when magic happens right in front of them in these movies.