The Mortumiasma looks like a cosmically large gaseous version of one of its Symbiotes.
The Mortumiasma is an apocalypse causing entity that exists in all dimensions. It is currently locked away via Ascalon, but if it were to be released, it would rapidly grow and destroy all universes. It has created the Symbiotes to be sort of heralds for it. The Symbiotes all have a hive mind, save for Unholy Smoke.
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