I've always gotten the impression that the physical world and the dream world are sometimes unstable. At the end of Ep.2 when we see Alexander and Manannan I thought that it was just a bit of a "glitch" in which Graham wasn't supposed to be able to see the dream world, but his drive to save his family gave pushed him into the dream world, at least for just a few seconds.
Frankly I've been believing that being in the dream world is some sort of Matrix thing where you can place your consciousness inside of the dream and, while it's just a dream and your consciousness, you can still die in it. That's why Graham was able to die to Shadows in the Tower Sequence even though he was in a dream at the time. If you let Shadrack kill Rosella in the dream world, Rosella would've immediately died in her bed.
My theory on Pandora's Box is that the actual Box wasn't there and that Shadrack created that area of the dream and a "dream Box" to make Valanice believe that she was opening the Box. If she -believes- that she opens the box in the dream, then in the physical world, the box will be opened. Since the physical Box is unreachable, the only way for Shadrack to obtain the physical one was to make Valanice "wish it" to happen in the dream world by using Rosella as bait.
I think that the spell ingredients were still necessary for Graham to enter the dream world even though he's been in it a couple times. He needs to go in there willingly and fully, not just for a few minutes because of "glitches."
I don't know though, I sorta lost track of the story where it was implied that Shadrack was Graham's pupil 1000 years ago