What has happened to Vana'diel? (Spoiler)

[Bhearil]

The shards are fragments of the source when it was sundered.

The crossovers for FFXV and FFXI etc that brought characters from that game or world over were actual dimension hopping from a multiverse standpoint. The version of Gilgamesh that appeared in the mobile game Final Fantasy Mobius actually broke the 4th wall telling your character about said multiverse referencing hero characters from games throughout the main series and when asked how many stories there were going to be said something like "about 15 not counting spinoffs and side stories."

Canon wise Gilgamesh is ALWAYS the same person, he jumps from one plane to another using the power of the Rift and he is a good actor being able to display several personas from serious to goofy. And yes is one of the most powerful characters of the entire franchise... when he feels like it since he tends hold back a lot in most of his personas

[Catwho]

Canon wise Gilgamesh is ALWAYS the same person, he jumps from one plane to another using the power of the Rift and he is a good actor being able to display several personas from serious to goofy. And yes is one of the most powerful characters of the entire franchise... when he feels like it since he tends hold back a lot in most of his personas

Yep, he's one of a handful of characters in the franchise that can universe hop.

* Aforementioned Shantotto (her mini expansion was her developing the spell and it backfiring)
* Aforementioned Noctis (likely due to an Imperial experiment)
* Lightning (not just during her crossover, but also during her actual game)

We've gotten hints that Y'shtola may eventually find a way to travel between the shards via magic. If anyone in the XIV cast would be able to find a spell to go beyond just the Reflections but also to other universes, it would be her.