Josef

Because, Gengar was the fist Ghost Type; Gengar is definitively a Ghost type right down to its name and origin.

There shouldn't be "complimentary" types. There is no other type that is considered that, so why should Poison be?

Poison Types have always felt like they've been given a back row seat; I mean hell, in Gen 6 we were given only TWO.

Flying.

It's like trying to headbutt a wall until it falls; I give up, it's waste of time to keep trying to explain it.