Invisible Scars

As Nightmare carried him away from the graveyard of horrors, Sunny managed to regain some of his composure. By then, they were moving deeper inland, following the light of the sacred staff. Effie was supposed to be at the end of that light.

As time passed, he couldn't help but think back to the Hollow Butterfly. 

The Great Monster must have landed on the hidden island a long time ago — but also only a few hours ago — to lay eggs. Then, it was caught in the time loop and somehow ended up with its soul destroyed. 

Sunny had never heard about a Nightmare Creature becoming Hollow, but it was not impossible. The question was… how had it happened? 

The obvious answer was that the gargantuan creature had been attacked by someone who could destroy souls. When a soul was destroyed, the body usually died with it… but on rare occasions, it survived. That was how Hollow humans appeared, so the same thing could have happened to this Great Monster.