The Essence that tore her apart too many years ago.
Eowyn saw it once more and with a refined brilliance as from the weapons that two Tribunal Rulers wielded, they struck down to heavily injure the whole fabric of the Dimension they were in!
This injury was a unique one as even with her remaining shackles, Eowyn could see its nature as she was once closely connected to the Dream Dimension.
She saw the vast and endlessly jagged gray rupture that seemed to stretch out endlessly pulse with the gray light- where it was actually proliferating over time as the sandy gold of the Dream Dimension became dimmer in the surroundings!
It was…actually generating this essence and spreading the gray light over time.
Frankly, it didn't matter from which position the Tribunal Rulers had done this in as eventually, this gray light would grow to infect the whole Dimension unless they could somehow combat it and stop its advancement!