Jin Wang encounters an old woman, toward the middle of the second story. After telling her about wanting to transform, she tells him that all he has to do to transform is

To forfeit his soul.

Explanation:

Jin told the old woman that when he grows up he would want to be Transformer. He explained this his decision as being "more than meets the eye". Which makes it seem like he desires to be mysterious and complex.

The old woman dramatically warns him, "It's easy to become anything you wish so long as you're for him to be willing to forfeit his soul.

From her words, It's easy for the boy to become anything he wishes to be so long as he is willing to forfeit his soul.

Refer below.

Explanation:

Jin Wang encounters an old woman, toward the middle of the second story. After telling her about wanting to transform, she tells him that all he has to do to transform is Forfeit his soul.