What the fuck is anti-soul gas?

*farts*
Well THAT is regular gas.

A general catch all term to explain when devs add a layer of fog to faraway objects in order to mask lower res textures or to render less polygons to improve performance, usually as a lazier way of handling things. While this was a common practice back in N64/PS1 times due to system limitations, it slowly faded away in the next gen, and has now since returned since it's a good example of developers not being able to optimize very well. Sometimes it's added to add "realism", but I wouldn't say fog is a natural phenomenon everywhere in the world, so it's more of a blanket excuse.

erm well BRAP

You know how modern games look really washed out like you are constantly looking through fogged up glasses?

yeah...