Edison format ruling
Shifting Shadows

Card effect (current official text)Once per turn, by paying 300 Life Points, rearrange the face-down Defense Position monsters in your Main Monster Zones, then return them in face-down Defense Position.
Rulings
- If you have only 1 face-down Defense Position monster you cannot activate the effect of Shifting Shadows.
- If you control a monster that is targeted by your opponent's Nightmare Wheel, and you flip it face-down with Book of Moon, and control at least 1 other face-down Defense Position monster, you can activate the effect of "Shifting Shadows". However, afterwards you must tell your opponent which monster is targeted by "Nightmare Wheel".
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the Edison forum — sourced change requests get reviewed.