@Serenata
Consider it a training arc which doubles as world-building.
@Baysiri
Honestly, it doesn't for the most part.
The benefits of these shadow worlds are more or less just 3 things.
1. they get stronger because they work like your typical dungeon where you get loot at the end of it.
2. they could potentially learn something about themselves or the past that could have significance if it's not set too far back in the past that drives the plot forward.
3. world-building slows down the tempo and fleshes out the story, though some could make the argument that it does slow it down TOO MUCH, it's up to personal preference tbh.
It's important to balance and to not have a too high tempo in your story, as it can ruin the story as a whole just as much as too much filler can.
@Legion_01
Creating material out of thin air is theoretically possible but not something we could do.
He might be using magic that drains raw energy from the world around him to create material out of thin air. ( its theoretically possible, but magic is always going to be magic ya know... )
His objective seems to be creating a truly immortal creature.