I found it by accident while investigating the strange lights at the top of the mountain and wasn't freaked out at all. I was enchanted. It gave me a sort of magical Princess Mononoke Forest Spirit kinda vibe. If you explore around Satori Mountain you'll find that it's bountiful and full of all kinds of resources. I think that the reason for that is the Lord of the Mountain. Like perhaps it's providing the mountain with life and energy. And if it's a tribute to Iwata then that makes it all the better.
Here's some screens of the LotM and the Forest Spirit from Mononoke for comparison;
The Forest Spirit also has another form later in the film and it has that sort of astral otherworldy look to it as well;
I'm fairly sure both entities have a tendency to walk on water as well, if I'm not mistaken.