"What are you doing here?" asked Newt as he stuffed his Niffler back in his suitcase. By the way, it turns out Newt's Niffler later becomes Mad-Eye Moody. This is canon now.
"Hunting beasts, just like you," Grimmson answered despicably.
"You're nothing like me!" Newt spat heroically. "You hunt beasts to kill them!"
"And yet, both our jobs are about to become obsolete," said Grimmson. "No doubt you've heard that Grindelwald is going after the Toenail of Icklibõgg. Unlike you, I will be happy to see my line of work disappear."
"How can you say that?" asked Newt. "Do you not realize how much we wizards rely on fantastic beasts? Why, we couldn't even make wands without phoenix feathers, unicorn hairs, and so on. I'd think that'd be something pure-blood fanatics like you would care about."
"Oh, Scamander," said Grimmson with an evil grin, "you lack vision. Once all the unicorns are dead, we'll be able to take all their hairs at once and make all the wands we'll ever need. We'll even be able to harvest all the unicorn blood, and sell it on an industrial scale. We could call it Immortium. Just imagine the possibilities!"
"If you're on board with Grindelwald wiping out the fantastic beasts, why are you even still hunting them?"
"For the challenge, of course. This could be my last chance to bag a real Mokele-mbembe. You know they live right here in the Congo."
"So, you hear that Grindelwald will be wiping out all the fantastic beasts in the world and your only concern is that this is your last chance to kill them for pleasure?!" asked Newt in disgust.
"And money," Grimmson agreed cheerfully.