I read somewhere else too about the feeling you get when a Gengar is near you

The temperature drops and gets really cold, and the breeze makes your hair stand on edge.
You can feel the breath on your neck, but you can't see anything except the dimming of the lights as you choke on the heavy density lingering in the air making it nearly impossible to breath.
You can't blink, you can't speak, you can't scream and you can't cry.