Alright, so here goes...
On this night of October, do beware! My child, you know naught what is there. Your sister may be lost to the darkness, my child. And, YOU may decide to follow her there.
You step into the clearing, closing in on the woman with the white hair. All around you, the shadows dance and the gentle winds cause you to shiver. Slowly, you make your way closer to her and reach out towards her shoulder.
Before your hand even touches her shoulder, the woman spins around and grabs your wrist, glaring at you with cold distant eyes.
"So, it is you," Your voice trembles as you speaks, and the woman's expression grows soft.
"Of course it's me," she chuckles for a second and softens her grip around your wrist.
As she speaks, it's like the rest of the world just vanishes, pushed away by the sound of her voice, and you remember the words your mother spoke to you just before she passed away.
"Katherine, do...do you even know that mom's dead..." You can feel a strange feeling pulling at your mind, "You've been gone so long,"
"I know, I know. I want to fix that." She smiles at you, gazing with her distant eyes into your own.
You can feel it happening...you can feel yourself changing. You know that your hair is changing color, you can feel your mind being altered. You close your eyes, crying. You don't want this....you don't want this...you do.
Everything's clear now, everything's okay. Your sister is standing there with her beautiful brown hair and blue eyes, smiling the world away.
"Come on, Helena can't wait to see you again! You know Helena right? Your crush?" She smirks and strolls into the warm welcoming darkness.
You blush, and laugh, chasing after her.
Edit:Yes I'm aware there's not much to it. It's a developing horror idea, that I've had (not this short clip itself [this is based on my idea of a sort of...changed person.]