Yes,Gengar Is based of a cartoonish ghosts, cats, or a Cheshire Cat,and possibly on a distorted shadow of a human being like shadow people.
Gengar's name is possibly a shortening of doppelgänger - a ghostly double of a person, which would be a fitting name for a Pokémon with a habit of pretending to be a person's shadow. The kanji 幻, which can be read "gen", can be used for words meaning "phantom" or "illusion". There is also a striking pronunciation similarity to the Danish word genganger - a person who returns as a spirit after death.
I love Weird things ¯(°_o)/¯