"TOR!"
The shock had clogged his mind, but Skyla's desperation freed the shackles in his mind. As he rewound time, he was panicking. He could feel the very edges of his soul becoming frayed from the level of fear and anxiety he felt after witnessing Kai's near death.
He had to think of a plan, seeing as the previous failed catastrophically. He could hope the ghast would flee into the forest. But then all of their work would be for nothing. They couldn't bind it more than they did, as far as he was aware.
He lacked the strength or reach to strike at its heart directly. Skyla was skilled at fighting from a distance. And despite the impressive feat of recreating her lost arm out of her own light, she was still not quite at the same level of fighting at close range.