Warning: Item description autism ahead
Who knows what lore will actuallybe expanded on in the DLC. My hopes are for an exploration of either the thematic connection between Godwyn's mermaid/fish/water stuff and the Malenia-Miquella duo through Malenia's mentor, the Blue-Cloth swordsman, or the possible connection between Miquella-Godwyn-Eclipse-Deathbirds.

In pretty much every Soulsborne game, "stagnancy"/"order"/"stability" are associated with decay and degeneration (the failing Age of Fire, the fall of the Healing Church, etc.). Elden Ring is no exception, with the decline of the Golden Order being the central plotline of the game.
Similarly (and more symbolically), Malenia's corruption is associated with stagnant water, via the Lake of Rot and the Swamp of Aeonia. Malenia's mentor, on the other hand, is tied to
flowing water, the polar opposite of stagnancy. The Blue-Cloth swordsman (who is blind like Malenia) taught her how to fight in this style of flowing water, inspiring the
Waterfowl Dance. And by fighting like flowing water, the mentor sealed away the Outer God in the Lake of Rot.
Blue Dancer Charm:
A cloth doll depicting a dancer garbed in blue.
An ancient heirloom of some sort.
Raises attack power with lower equipment load.
The dancer in blue represents a fairy, who in legend bestowed a flowing sword upon a blind swordsman. Blade in hand, the
swordsman sealed away an ancient god — a god that was Rot itself.
Flowing Curved Sword:
Legends speak of a master of the sword garbed in blue, and his curved blade that was patterned after flowing water.
Strong attack unleashes a series of strikes akin to a dance, offering a glimpse into the legend.
Prosthesis-Wearer Heirloom:
A talisman engraved with a scene from a heroic tale.
Raises dexterity.
Though born into the accursed rot, when the young girl encountered her mentor and his flowing blade, she gained wings of unparalleled strength.
Blue Cloth Cowl:
Cowl of a nomadic warrior.
The blue color of its fabric symbolizes brisk waters, as fluid and flowing as the sword in the hand of its wearer.
Just as still waters turn foul, stagnation leads to decay.
Warriors must remain ever-drifting.
Malenia and the Scarlet Rot are not the only corruption in Elden Ring associated with stagnant water. It's been discussed
ad nauseam that Godwyn and Deathblight are associated with water (Godwyn is a gross fish man sitting in a filthy puddle, Deathroot by ponds, Tibia Mariners, Deathblight Crabs by the Leyndell moat, etc.). Not just any water; specifically, the Deathblight is primarily associated with
still water. I'm not much of a weeb, but my understanding is that in Japanese folklore, stagnant water is a symbol of corruption, death, disease, and rot, which explains why both Scarlet Rot and Deathblight would have a standing water connection. I also think that it is no coincidence that Godwyn, even as a fishman, is always depicted wearing a blue-cloth sash.


(More of a stretch, but I don't think it's a coincidence that Malenia and the Blue-Cloth Swordsman are/were blind, while Godwyn and Deathblight are associated with clouded, seemingly-unseeing eyes. Also, the Godwyn under Stormveil Castle seems to be missing its eyes; the eyelids cover empty sockets.)
I wouldn't be surprised if Miquella was equally inspired by the Blue-Cloth swordsman who helped his sister seal away her stagnant rot, and that is why he hoped to free Godwyn from his stagnant-water undeath. There is plenty of lore showing that Miquella had the goal of freeing Godwyn from his current state (and anyone who says there is no lore connecting Miquella to Godwyn is smoking crack). The Eclipse Spirit in Castle Sol (Miquella's fort) has this to say:
Ohh great sun! Frigid sun of Sol! Surrender yourself to the eclipse! Grant life to the soulless bones!
The Spirit at the end of Castle Sol has this to say:
Lord Miquella, forgive me. The sun has not been swallowed. Our prayers were lacking. Your comrade remains soulless. I will never set my eyes upon it now, your divine Haligtree.
The Eclipse Shotel, one of the major rewards of Castle Sol, has the "Death Flare" Ash of War, referencing Godwyn and Deathblight.
Set the lusterless sun ablaze with the Prince of Death's flames, inflicting the death ailment upon foes.
Finally, the Golden Epitaph makes pretty clear that Miquella wants Godwyn to be freed:
A sword made to commemorate the death of Godwyn the Golden, first of the demigods to die.
Infused with the humble prayer of a young boy; "O brother, lord brother, please die a true death."
Given that the DLC is clearly Miquella-heavy, I would be shocked if we don't get
something related to Godwyn and the Eclipse. This post is already long and autistic enough without in-depth rambling about what exactly the Eclipse
is, or what endgoal Miquella has. Maybe it's as simple as that the Haligtree was meant to "eclipse" the Erdtree, tying into the two intertwined trees in the DLC. There might be some connection to the Deathbirds and their relatively unexplored lore. (There is a Deathbird right by Castle Sol, and they were associated with rituals to "cleanse"/burn death through Ghostflame.) Or maybe the DLC tree(s) are the "lampwood" that "guides the dead of the spirit world," referenced in the description of the Helphen's Steeple greatsword dropped by the Tibia Mariner overlooking Castle Sol.
Or maybe Miyazaki will strike again, and the DLC will have basically no connection to the unexplored lore from the base game.
