Behind the fake, Hugh was Aric who stood there with his arms protruding from the monster's stomach.
*SHHRKK*
Aric pulled out his hands from the monster and green blood immediately started to gush out. The monster's innards were destroyed as Aric used his black fire to freeze and disintegrate most of them.
There was no other way that he could have damaged the creature. This was the only time where the creature was vulnerable.
He needed to take a chance when the creature could not phase through his attacks. And that time only came when the creature was attacking.
Aric only figured this out as Jane was fighting the creature. He saw that when the creature had its leg inside and stuck on the floor, it could not move, or else it would be attacked by Jane's attacks.