So... mini nuke through the process of thermal expansion? He kept the rock cool while compressing the heat the surrounding of the rock in order to avoid melting it. Once they mixed after it left his control, boom?
I think some character progression was rushed and he somehow went from wanting to participate to not wanting to participate to wanting to participate over the course of like three panels. @Wolvenworks
This was better in the earlier chapters when I thought it was going to clever use of his ability to do specific things to alter the fight
I keep on getting amazed by how stupidly powerful the microwaves in this world are. They can literally evaporate mountains if you leave the lid open as they are running?!