This is part of the DragonSoul continuity.
This was the legendary battle between Danny and The Lich over the fate of the Multiverse in 25492.
Danny won it by finally letting go and entering his Ultimate Form. He spent years destroying the then immortal Lich in various ways, before banishing him to the core of the planet.
Afterwards he regained his humanity and became the new First God, recreating the universe as a final act before becoming raw energy.