Pitch Black:

He wasn't stupid. He could read what the Man in the Moon was saying. And Pitch had an advantage; he already knew exactly who one of the new Guardians were. If he got to that Guardian in time, before the others did, then Pitch would have that power on his side.

After all, the Guardian Of Autumn would be able to make things die at his touch, wouldn't he? And with that kind of power, so much more fear could be created. The threat of the boy and a dragon being able to murder someone just by touching them, would be amazing.

Pitch just needed to get his hands on the boy.

Through the boy, he could get the other three Seasons Guardians who he knew existed. Pitch would be able to have Jack at his feet, begging for mercy. Gothel would get her flower back, and Mord'ue would get to murder the Summer one for whatever reason he wanted.

And so Pitch started to formulate a plan to get the Autumn Guardian on his side.