If he hadn't been slowly sliding back to his prior mindset, he would have retreated. He recognized that this thing was dangerous, especially with the sheer wrongness of its very presence. But with the reawakening of his past self, his refusal to take any resistance kept him in place. This was akin to Giratina and he would defeat it, he HAD to defeat it.

"Houndoom, Will-O-Wisp."