Firesword was the personal lightsaber combat form of Greyst Denali. It was the mixture of all of the strengths of every single lightsaber form he had mastered. Essentially, it was all of the strengths of every single lightsaber combat form without any of the weaknesses. The only weakness was that it was a mentally draining Form. A person who didn't have a very strong will would become mentally exhausted by trying to learn or use the form, since it required immense concentration.