Answer:
Useful tool for who in darkness dwell. Within you, corrupting like a deadly spell.
When the horse strokes the cat, the wood begins to sing.
There is someone, and there is always another, for without the other, there wouldn't be one
Always wax, yet always wane: I melt, succumbed to the flame. Lighting darkness, with fate unblest, I soon devolve to shapeless mess.
Green arrows grow out of my sides. I go from yellow to white. My babies fly in the wind. What am I?
In birth I spring forth, in life I unfold. In death I wilt and die, but rebirth restores all.