You have to keep the wardens you want to kill alive (solar shield if you want raze lighter, void shield one if you want dark drinker, arc shield one if you want bolt caster, and you can kill the wardens you don't want) until you have the Darkblade low on health (like, just below the first "A" in Alak-Hul) then you quickly kill your wardens [b]first[/b] and then the Darkblade within 30 seconds of each other.