Mirror ethereal island concept
(It’s not split half-and half, it’s randomly scrambled)
basically, my my concept, what caused the mirror pocket dimension to tear open was Zarroë getting a bit too daring in one of their experiments in the workshop, and it had an odd effect- the colossal themself had become unstable! Their newfound instability tore open a hole in the pocket dimension. But that wasn’t their only issue- their body was scrambling a rearranging its parts, rather concerningly fast.
With their ribs boring through the back of their head, their nerves ending outside their body, and their eyes peering backwards into their skull, they…weren’t having a great day