Blibdoolpoolp - An insane sea goddess worshiped by the equally insane kua-toa. It is said her very gaze causes insanity and she could easily fit into Nyarlathotep's "Crawling Chaos" moniker by being heralded by swarms of small crabs.
Oddly enough, a neutral god there fits the bill: Zivilyn because of this: "Zivilyn encourages self-knowledge and enlightenment even though it may be through either tranquility or madness."
What D&D Dragon-Lance, Forgotten Realms, Eberron(etc) Deity is the closest to Nyarlathotep?
Look for a Deity that drives people mad, because he is bored(just like my son).
Some options:
Forgotten Realms
Conversely, it could just be some alien entity and look like this:
All options below are optional. But a quick trip through memory lane...
Forgotten Realms, I would look at:
Dragonlance:
Greyhawk:
Eberron: