This is a small theory I've had about DkS 3. A few weeks ago, I was watching a video that was showing and talking about the gameplay that had come out (I think the video was by terra mantis). In the video, he speculated that the giant hand coming out of the tree was possibly a dragon. He brought up some other points such as the reason the arch trees were burned in the dragon war was because dragons were born in them. I was watching some of the beta gameplay and when that one undead turned into that weird creature, I noticed that its mouth was strangely reptilian, almost like a dragon. And the undead seem to turn into trees. So what if that undead had a dragon embryo put into it because it was going to turn into a tree, but when we came along, something caused the now dragon fetus to burst out and attack us. It could have been implanted by one of the other dragons that appeared in the beta. But hey thats just a theory.
Some new Dark Souls 3 screenshots