When Riker was sucked into Armus, Jonathan Frakes was in fact submerged in a pool of Metamucil and printer's ink. During a break in filming while Frakes was lying on the beach, covered in the sludge, LeVar Burton approached him and said "Frakes, I never would have done that!"
In his online review of Star Trek: The Next Generation: Hide and Q (1987), Wil Wheaton commented on how in the first season that Michael Dorn as Worf, didn't do much more than Denise Crosby did and that Worf was, according to Wheaton, "one dimensional and so incredibly stupid," but eventually Dorn was able to develop Worf into a much more complex and beloved character, whereas Crosby, out of frustration, just quit the show.
For the scene where Riker is pulled into the oil, a stuntman was used as a stand in for Jonathan Frakes. Where Riker's face emerges from the oil, it was actually a plaster cast of Frakes' face painted black. It was placed on the same grate used to lift Mart McChesney, and filmed lifting out of the liquid.
In describing TNG Season 1, and Gene Roddenberry's attempts to "push the limits a little", Jonathan Frakes stated, "I think we took greater chances then than we do now. The shows may be better, the level of it, but "Skin of Evil" was absurd. We had Patrick sitting and talking into a black oil slick- but what was wrong with that? I suffered physically like a fool with Mikey- sure, I'll get in that black fucking Metamucil shit. That was absurd."
Armus was originally intended to be based on the Mummenschanz theatre group style, but was discarded in favor of a "shroud" type creature. Joseph L. Scanlan was determined to make the creature believable, and it was aimed to have the creature rise up out of the oil slick, drawing it up with him. A test was made using a melting miniature figure of Armus with the intention to play it in reverse, but it didn't provide the required effect. The construction of the suit for Mart McChesney to wear as Armus was split between two teams. Michael Westmore and Gerald Quist spent a day sculpting the head, while the construction of the body was outsourced to an external company. McChesney as Armus was lowered into and out of the oil by means of a grate under the surface. Although the head was designed to enable the clearing of McChesney's airways quickly should there be a problem, no oxygen tank was included in the construction and so he had to hold his breath whilst under the surface of the oil. Crewmembers kept track of the length of time he was under by using a stopwatch. The oil itself was a water-soluble Metamucil material which was dyed black using printer's ink. During production the crew found that for some reason the liquid kept dissolving the seams of the suit, although the head was unaffected. A backup suit had been ordered before production began at the last minute, and was required in order to shoot all the scenes. After they started to break apart, further orders were placed for additional suits and all the suits used eventually fell apart during the four days they were used on set. In order to film one scene, McChesney wore the suit open-backed due to the damage.
The trivia items below may give away important plot points.
In the original production order, Skin of Evil preceded Symbiosis. The order was changed because Denise Crosby had asked Gene Roddenberry if she could remain on the show for Star Trek: The Next Generation: Symbiosis (1988). She had gotten a hold of the script, and thought it was interesting, so she asked if her character's death could be delayed for one more episode. Roddenberry granted her request, and had the airing orders for the two episodes switched, so there would be no continuity issues. This explains why she's waving goodbye at the end of Symbiosis, her last filmed episode.
There was some debate among the writers over the final fate of Armus. Gene Roddenberry ultimately mandated that Armus not be killed, believing that as human beings, no final moral judgment be made on any creature that was encountered.
During FanExpo 2007 in Toronto, the guest speaker, Jonathan Frakes, spoke of how sad the cast was to see Denise Crosby leave. Frakes told an anecdote of while they were shooting the final holodeck scene for Yar's funeral, Patrick Stewart jokingly lightened everyone's mood by singing "The Hills Are Alive" from the musical "The Sound of Music" as they were walking up the grassy knoll.
Yar's memorial scene was filmed twice, the first was with Denise Crosby reciting the lines while looking straight ahead, which was the director's preferred choice. However a version with her looking towards each of the other characters in turn was ultimately used. Joseph L. Scanlan later said "Don't ask me how she knew where they'd be standing".
Most involved with the series felt that this episode was an unmitigated disaster; not only did they have problems making an oil slick a believable character, but they felt that the death of Tasha Yar was a low point in the evolution of the series.
Jonathan Frakes recalled of Denise Crosby's departure, "That was sad. The day we finished up filming that last show. She'll really be missed. Denise and I used to dance around the set between takes and sing together. She really brought life to the set. It's ironic, that they finally came up with a script that gave Tasha great things to do, and it was the one where she died. She shot her farewell message to us in one take."
On leaving the show, and marking the end of Natasha Yar, Denise Crosby stated, "Gene really felt that the strongest way to go would be to have me killed. That would be so shocking and dramatic that he wanted to go with that." At that time, several rumors had been surfacing that Gene Roddenberry's lawyer, Leonard Maizlish, was rewriting a majority of the season's scripts, an illegal act in terms of Writer's Guild policies. According to one source, Maizlish was responsible for the dismal manner of Yar's demise, and wanted to be sure that Roddenberry's story idea was enforced, and that Yar's death happened as a matter of course during a dangerous mission, despite the differing views held by the various writers involved with the story. In the end, there was considerable controversy among the show's staff regarding this death: some felt that it was cynically manipulative, while others felt that a swift death made sense to avoid sentimentality. In retrospect, Crosby added, "perhaps Tasha should've really gone out in a blaze of glory. There's never any real battles ever fought. The show is never supposed to be about violence and it shouldn't be. But I think if you have one cause for there to be a show about a real violent battle, that was it. Let's see this supposed expert security officer do her stuff."