Before we acknowledge the elephant in the room, let's address the episode equation. If you count S1E1 (the pilot) as one episode, Skin Of Evil is indeed E22. If you consider the two-part episode as two separate parts, then this would be E23. As I streamed it on Paramount+ and the first episode was one continuous episode, I consider Skin Of Evil E22. Right. Onward.
"Save your pity for yourself!"
Skin Of Evil is hands down my #1 favorite episode thus far into the series. *spoiler alert* Most consider the unexpected death of Lt. Yar as being the point of contention of this episode, but I have never been a big fan of Denise Crosby, so I never really warmed to her character. Armus, the big black goo monster, is definitely the highlight for me. I couldn't help thinking how this is a perfect mash-up of Stephen King's The Raft and Star Trek. He's not evil, he's just lonely and bored! He's cranky and just wants to be entertained. He can't help it, he's made out of pure negativity after all. But the way the voice is articulated, (and those screams!) I couldn't stop giggling throughout all of his scenes. Hee-larious!
If you want a rational and somewhat technical explanation of this episode, have a look at this You Tube clip: