Question

I need it all I need is to see it

Answer 1

A trainer in Victory Road has a Gengar.

Answer 2

Or you can see gastly/haunter in a tower under solaceon city or in a house in eterna forest! just evolve it...

Answer 3

If you have a certain game(I think leaf green of fire red) in your gamboy slot, and go to the old chateu, in the room with a picture, you can find wild gengar.

Comments

It's definitely either FireRed or Ruby because those are the two I have and I found the Gengar. Most likely FireRed since Gengar is in that game.