Gravis had no more plans that could guarantee his success. This fight felt similar to his battles with Red and the priest in the Heaven's Trial. Back then, he also had no idea how to win. Only through finding an opening or a new path had he been able to prevail.
Yet, Gravis really had no idea what he could do now. His Battle-Strength was just too low. The biggest issue was the opponent's defense since he could shrug off even Gravis' most powerful attack. As soon as he transformed into metal, Gravis' Lightning Crescent would only be able to melt off some parts of his body.
Yet, the Golden Dragon had a length of over five kilometers. Even if Gravis managed to melt off a hundred meters, he would have only given the Golden Dragon a flesh wound. In order to damage the Golden Dragon's organs, Gravis would need to melt off way more than that.