Here’s how I see Part 4 breaking down:
Gaspar hits Belfan like a ton of bricks (changing the map up enough like the Dreamworld does in Part 3) and aims to destroy the Aether Crystal at the heart of Belfan, wiping out the planet as well as Mardek, Rohoph, and the “Resistance”.
The dungeons would be:
*The area Gaspar blew up (the starting area)
*The Sky Temple (for the Air Crystal)
*A new part of the Sun Temple (for the Light Crystal)
*A confrontation with Muriance/Steele for the Dark Crystal (maybe even causing Steele to join because of Muriance taking the Crystal from him we don’t have a permanent Dark ally yet).
*Aether Temple/Belfan’s Core: Where the fight with Gaspar happens, using the six Crystals to stop him…
*And of course, a fight with the Heroes at some point.
Epilogue: I don’t think Rohoph having all 7 Crystals will be a good thing…