Board Thread:General Discussion/@comment-31760473-20181212174444/@comment-30314236-20181227224527

So in the ancient list Ootakemaru is the last one of the Three Great Youkai of Japan, and in some point of time he was replaced with Sutoku in a new group known as the Three Terrible Youkai of Japan. And in this new group, Sutoku is a tengu and not an onryo (from what I've seen on the net). My bad, I actually meant the latter group and mixed them.

I looked into that reddit post and it is also mentioned that Nasu created another separate list: the Three Great Metamorphosis of Japan, which only Tamamo is known among them, excluding the other ones.