[Black Plauge] Can't move on (potential spoilers)

[darkely]

I am at the part where you get the crystal and go to combine all the materials but I am stuck... there is nothing on the to-do list... where do I go now?

as always no spoilers if they are needed use the spoiler wrap ([spo!ler]blah blah blah[/spo!ler]) replace the "!" with an "i".

video...