During the time we had to prepare before combat, we had countless discussions.
"Elemental clones from splitting? Destroy them with temperature differences between hot and cold."
"Diamond-like impenetrable body? That's possible. Adjusting his own elemental structure and transforming into a harder substance seems likelier and likelier the more I think about it. What should we do in that case?"
"Diamond-like structures are actually easy to deal with. Their solid structures also mean that they're more afraid of structural change. Temperature differences will change the structure, as it typically won't be able to stand up to high heat. We'll just have to bake the entire battlefield. I'll go find the goblins and prepare some extra top-level oil."
"Is transforming into a tremendous giant possible? Don't the final bosses in stories always suddenly have a bigger form at the end…"