Palace of the dead lore?

[WhiteArchmage]

So, the items you can get are the Firecrest and the Glass Pumpkin, I don't remember a dragon soul (though Dragons ARE involved in PotD in the Ogre saga, more on that later)

The Firecrest is an important item in the Ogre saga, being a relic used by the hero of the mythical Ogre Battle (not the game of the same name, rather the battle against the underworld in the backstory). Destin Faroda, the hero/ine of the original game, can find it but doesn't know how to USE it. Denam Pavel (Tactics Ogre: Let Us Cling Together) and Alphonse Loeher (Tactics Ogre: The Knight of Lodis) can use it as the Ultimate Accessory. Never played Ogre Battle: Person of Lordly Caliber so idk if it's there, too.

The Glass Pumpkins are tied to the PotD: they show up there and are also connected to the legendary Witch Deneb: In LUTC, you need to sell her 30 pumpkins to recuit her in her special Wicce class. In TKOL, you need to sell 5 to her shop to get the Firecrest. And in March of the Black Queen, she gifts you one after a side-quest (the item lets Witches recruit Pumpkinheads, Deneb's recurring minions, and VERY HEAVILY IMPLIED to be young men she kidnapped and replaced their heads with pumpkins in MOTBQ; in the other games they're implied to be pumpkins she gave life to with magic).

As for Dragons... well... this is the part that's likely completely unconnected to XIV. The PotD in LUTC was originally built by the Dragon Lords, and their legendary forgemaster made most of the machinery inside. As such, the PotD is especially known for studies into necromancy and dragon magic. Which... is completely against what we know of dragons in XIV. One thing that likely DOES carry over, is that the lowest floor of the PotD is Floor 100, where Nybeth holds his altar, and on that floor (floor 114 in the remake) there is a portal to the Abyss/Underworld (named a Chaos Gate). PotD was originally named Hellgate in the SNES release.

I COULD theorize that floors 101+ are indeed in the Abyss/Underworld, with Floor 200 being a floor of respite as the abyss acknowledges your strenght and lets you go (something that doesn't QUITE happen in LUTC... in the remake, you go to the lowest floor rescue one of your allies that sent himself to the Underworld for reasons... which considering he used the OTHER Chaos Gate in Valeria to get to the Underworld...). But that is purely speculation based on the different layouts Floors 101+ can have.

Edit because I can't believe I forgot this detail: Chaos Gates don't just connect to the Underworld, they also serve as gateways to HEAVEN. The 3 Dragoons in Ogre Battle: MotBQ are found on Floating Islands connected by Chaos Gates, those "Sky Islands" served as their place of retirement after the Ogre Battle, since they were barred from Heaven thanks to Fenril giving humanity her sword Brynhildr (which is a plot point in several of the games). This is again just theorizing, but the portal from floor 199 to 200 could indeed connect to a sort of Paradise of tranquility before you leave the Palace.