My theory for Sigmascape

[Yitan]

snip

To be fair, I'd love if they used the original Four Fiends from FFI or IX (Lich, Marilith, Tiamat and Kraken). Technically in the remakes of FFI Omega and Shinryu are in the game, and due to the fact that they can literally travel through dimensions, impossible is nothing?

The only problem I see with these Fiends is the fact that Tiamat is already in the game and she's sealed "forever"? And Kraken is dead after Sastasha HM.
Lich would be a badass boss in O8S and Marilith would make a great "petrification" boss, like a SCoB T7 part two lol.