Silver Dungeon

I came across a silver dungeon while i was exploring the aether and i went in and killed all of the chest monsters but for some reason i cannot seem to "provoke" the valkyries and i can't attack them without them dissappearing. in the aether thread someone said to use a diamond sword but no matter what i try i just can't get them to fight me.

if anyone could help me out that would be great

Go off Peaceful.