The Gastly Family
I'm sure this has been one of the most anticipated of them all. Almost everyone loves the Gastly line, the only "ghost" type pokemon in the original 151, even if they've long since been outshined by the weirder and wilder depths of the game's spooks.




The Gastly Family
It's funny how Gastly comes immediately after Cloyster, and basically has the exact same face. This lead a lot of people back in the day to speculate that Gastly was specifically the ghost of a dead Cloyster, which is still interesting enough for me to support, though it seems more like the majority of "ghost" pokemon aren't really the spirits of the dead at all, but creatures who naturally exist in an intangible, extradimensional state.

Like Cloyster, I also feel Gastly's solid orb design wasn't meant to be its "official" anatomical plan, but something adopted for its pure functionality. Gastly is supposed to have a completely gaseous form, and that's communicated beautifully by its very oldest in-game sprite.
This "gaseousness" is also the only rational reason for Gastly to be part poison, besides my personal theory that poison typing was just slapped onto every "scary" pokemon in the first generation. That our only ghost/poison pokemon has basically nothing to do with poison bugs the heck out of me, because a thematically toxic ghost is an awesome concept with enormous design potential. Why not a poisonous ghost made of dripping acid? A poisonous ghost made of reeking garbage fumes? A poisonous ghost that looks like a tattered haz-mat suit? Come on, Pokemon. It's been twenty years and your only biohazardous phantasm is something that only communicates its "ghost" aspect.

Is that not cool as heck? Early Haunter had a more rounded head-body and a more jagged mouth, more like a carved Jack O' Lantern face in the dark.
We can see how Haunter follows logically from Gastly, of course; it's still only semi-corporeal, but it's on its way to forming a more solid body out of Gastly's misty form, or rather, manifesting itself further into our own dimension!
I feel very strongly that Gengar was originally conceived as a pokemon capable of taking almost any conceivable shape, and had they the technical capacity, manpower and budget, the original games might have provided it with multiple, alternate forms all along. The Clefairy-like shape was simply chosen as a convenient, default example of a creature with many possible configurations, and by the time the games had a capacity to reflect Gengar's true concept, this design had already been cemented as its most official.
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