Final Fantasy IX content

[Seraphor]

The Mhachi raid series has quite a lot from IX.
Firstly the whole weaponising an army of black mages is an allusion to the black mage army in IX, with several parallels between Mhach and Terra.
The whole airship/sky-pirate thing, although similar to XII, is actually more closely related to Tantalus.
Void Ark's design is quite similar to Pandemonium on Terra.
The Mhachi's teleport pads are similar to the Terran teleports.

The theme for Weeping City includes part of the IX battle theme.
The 'Weeping City' itself being an allusion to Burmecia.
You fight Ozma near the end.
And then the Nullstone that the raid is based around with you obtaining it inadvertently for Diablos, is similar in concept to the Gulug Stone that Kuja tasks you with finding in Oeilvert. Both magically sealed away by the former civilisation.

Dun Scaith features Deathgaze which featured in IX and the 3rd to last boss.
Again, an airship assault in the same style as the airships from IX.
The city of Dun Scaith itself draws some design parallels with Kuja's desert palace.

None of it is too direct, but it's kinda similar to the Eden raids and VIII, with how Fatebreaker is a parallel to Griever, with the theme of Gaia losing her memories, etc.