Why did the Drakh emissary look so blurred in S04:E11 “Lines of Communication”?

De acordo com a esta postagem on the B5TV forums, JMS had the following explanation:

The Drakh emissary is described in the script as a servant of darkness, who causes lights to dim as it nears them as if sucking the life and light out of everything it passes. In the episode, an effect was added in postproduction that turned it into a blurred, indistinct figure. "I had everything darken when he comes near it because I was so burned with the 'Infection' situation and the 'Grey 17' thing," explains Joe Straczynski. "I said, 'I don't want to do another obvious guy in a rubber suit so let's keep this dark and shadowy.' Of course, it was shot nice and bright, and also the paint job on the actual face wasn't what I wanted it to be--it was the wrong color, and it ended up looking like a mask, instead of looking like a breather unit. I thought, 'well, look, these guys worked for the Shadows, they would have some access to Shadow technology, and we know the Shadows can phase in and out of appearance. Why can we not make the logical extension that they have adapted a system which keeps them blurry a little bit?' They really can't be seen clearly and thus, become more ominous and, thus, more frightening to the average passerby."

So, in the original script, there was no blurring effect, only the dimming of lights and so forth. However due to problems with the makeup and other effects, they elected to throw the blurring effect in to help sell the Drakh as a mysterious and alien threat. JMS's post-hoc explanation was that the Drakh were using a Shadow device of some kind, possibly for intimidation purposes (since it doesn't seem to hide them very effectively).

For what it's worth, none of the other episodes that featured Drakh had a similar effect in either B5 or its spinoff Cruzada, and it was never conclusively demonstrated that they were even the same species as the "emissary" seen in "Lines of Communciation".