"It's a simple choice, Scamander," Grindelwald said perfidiously. "Either your girlfriend dies or you agree to help me locate the Toenail of Icklibõgg."
"Oh, about that," said Newt. "The Toenail of Icklibõgg is gone now."
"You're lying," said Grindelwald. "There's no way you could have destroyed it already!"
"I didn't. It was my brother Theseus."
"Darn it, who could have guessed that the one named Theseus would defeat the Labyrinth on Crete?"
"So, you see," said Newt, "there's no reason at all for you to do this. Just let Tina go."
"Not so fast, Scamander. You've been a thorn in my side for a long time. I can't believe I keep getting beaten by a bloody zookeeper! The only thing more humiliating than this would be getting repeatedly beaten by two heroic Hogwarts students and their silly redheaded friend. Of course, that would never happen to any self-respecting Dark Lord."
By the way, it turns out Grindelwald's absolute favorite movie was The Gold Rush, so much so that he was planning to spare Charlie Chaplin when he got around to exterminating the Muggles. This is canon now.
Anyway, Grindelwald held out his evil hand to Newt. "Join me, Scamander, and together we will work together to achieve immorality!"
"You mean immortality," Newt corrected him.
"Whatever."