Quite a few Pokemon would outright kill anyone standing close to them, whether it's ones with skin hotter than the surface of the sun, ones that burp at a billion decibels, or ghosts that continuously absorb the souls of everyone they look at. A bit of toxic gas is nothing.

That has to be bad research on Nintendo's part. Wouldn't his skin be absolutely blinding, like the sun or another star? Not to mention that it would make the temperature rise extremely, the earth would probably be destroyed the instant he existed

Koffing and Wheezing are much more realistic, relatively speaking