It certainly wasn't the most efficient way to use mana, but it could do the job since it killed three tyrants instantly. In the end, Meryl was also a very sentimental person, so she couldn't let herself fall behind when the one who would benefit the most from that operation would be her.
Meryl continued to use the bones of the tyrants in many ways, such As arrows, spears, and even traps, to hinder their mobility. Billy didn't know if that was her second skill, but it certainly was a skill that granted her the power to control bones as she saw fit. It was pretty weird but effective when used alongside those types of monsters since their whole bodies are strong and hard as steel.
