Question: dark souls 3 how to make vordt's great hammer?
Answer: To transform a boss soul into a weapon/spell/ring, you have to get the Transposing Kiln from the Curse-Rotted Greatwood (Undead Settlement boss) and give it to Ludleth of Courland (the guy who sits on the throne in Firelink). Once given, you can trade your boss souls with him.