Couple of things LeeRoy is probably going to ask:

How strong does he become in the presence of The Dragonslayer, and how much does it harden his skin? Stating that he is as strong as a younger wyrm does us no good, as we do not know how strong that is.

What kind of toll does Ragnarok take on him, and how long can he keep it summoned?

You mention that it burns twice as hot as normal fire, but what materials is the standard fireball capable of igniting (since it wouldn't have a fuel for a reference to determine temperature until it ignited an object)?

My own questions:

Where is the center-point of the fire dome? If it's on the ground at his feet, his head would get burned off every time he used it without crouching (since the bio doesn't mention any special resistance to the flames).

How quickly can the sword take a new form, and is there any kind of a charging/recharging mechanic to it?

How is the fire countered, if not by dousing or starving it? Even his least powerful spell would be able to burn until everything around it was ash, and if it ignited a person, it would only be a matter of time before they die or have to cut off the burning portion of their body. That seems too powerful for a tier 4 character, considering that all he would have to do is hit a tier 7 with one fireball then walk away and wait (or he could potentially burn down the entire arena just by flaming one tree).