Se acontecer que não há conhecimento sobre gloomblades independentemente das aventuras de AL que já referenciei na pergunta, parece que o conhecimento apresentado em DDAL06-02 A redenção de Kelvan is a única fonte oficial que contém qualquer conhecimento (desde que DDEP06-02 Return to White Plume Mountain apenas referencia os eventos do outro módulo, sem conhecimento adicional).

O módulo afirma que um gloomblades estão

perverted mirrors of the elven moonblades. Longswords made from a piece of frozen darkness brought from the Shadowfell [...] The sword is likely tainted by evil — reflective of Shar’s mission to unmake the world.

-- DDAL06-02 The Redemption of Kelvan, pg. 5

Também afirma que

the magical gloomblade, [is] a sword blessed by Shar with powers over shadow and time

-- DDAL06-02 The Redemption of Kelvan, pg. 3

E ao manusear a lâmina:

Any character picking up the sword feels a deep sense of despair and emptiness, as if all hope has drained from them. It is horrible to carry and no living soul would be able to bear it for more than a few days. The sword has no magical abilities that the characters can access at this time.

-- DDAL06-02 The Redemption of Kelvan, pg. 12

Então, em resumo,

gloomblades are longswords made from pieces of frozen darkness from the Shadowfell, likely tainted by evil because of the fact that they are "blessed" by Shar, although that it says "likely" implies that they might not be, though the implication is that they probably are evil. They resemble moonblades, but given that they are made from darkness from the Shadowfell, likely are not actually corrupted moonblades, but are rather created to resemble one. Gloomblades are horrible to carry, unbearable for more than a few days, since they make you feel a deep sense of despair and emptiness, as if all hope has drained from you.

Pelo menos, é a minha opinião sobre as informações apresentadas em DDAL06-02 The Redemption of Kelvan.

Also, interestingly, since it seems that they aren't actual moonblades (since they were made from frozen darkness, etc), they might not actually be sentient like moonblades are, since the module doesn't explicitly say that they are, but now we're into speculation, so I'll stop here.

Sim (mais ou menos)

A partir de Pathfinder Ultimate Equipment:

Gloom Blade

Aura strong evocation; CL 13th; Weight 2 lbs.; Price 8,810 gp

DESCRIPTION

As black as coal, this short sword grows more potent the farther it is kept from light. It acts as a +1 short sword when in dim light. In darkness, it acts as +2 short sword. When surrounded by supernatural darkness, such as in an area of deeper darkness, it acts a +2 short sword and bestows the benefit of the Blind-Fight feat on its wielder. In daylight or bright illumination, the sword temporarily loses all its magical enhancement bonuses and acts as a masterwork weapon, though it resumes its magical functions once it is no longer in the bright light.

CONSTRUCTION REQUIREMENTS

Feats Craft Magic Arms and Armor; Spells deeper darkness; Cost 4,560 gp

Nota: Conforme discutido em esta pergunta no Pathfinder, não é estritamente D&D, embora seja um derivado direto sob o OGL.