Full art:

Wings:

“Because the wings on its back have grown large enough for it to fly, the wings on its ears have regressed”

Claws and spikes:

“Part of its claws and spikes have turned into obsidian”

Floating skulls:

“Reference for the grudge effect”

Appearance without the miasma:

Source.

As a side note, the Japanese name for the monster is revealed for the first time: 滅亡き闇　ヴェイドス (metsunaki yami veidosu, most likely). The first two kanji form the word “metsubou” which translates to “destruction/extinction”, possibly relating to what the Japanese name for Veidos the Eruption Dragon of Extinction may look like. However there’s a play on words by using the second kanji as “naki”: It would become a negative modifier to the first kanji, “destruction”, which would make it a word like not-ending, not-extinguishing or non-destroying. Polishing it a little, it would be something like “Veidos the Endless/Inextinguishable/Indestructible Darkness”.