Beat me to it, woohoo!
Here's my version of the save:
As some might say, having two in the hand makes a gooey mess:
TOS Season 3: “Day Of The Dove”
Never mind the bush they're cooing on, which will probably bloom brighter next spring as a result.
So, the unknown space swirlie thing enemy lives off the emotions of other beings. Did it originate on this planet they were visiting, or do they live in nebulae and only go to planets out of abject boredom (but for now, I'm keeping it focused to being a terrestrial life form for now)? Is it a rogue? Just vacationing where there's not even a hotel? Last of its species? Even "Skin of Evil" provided a solid backstory to explain the alien fritter while leaving more open-ended (the discharge of a large and otherwise nondescript species believing that shedding all its evil would make it better, interestingly...), yet this is just one swirly thing in space that is red when feeding and pale when it's starving. Nice detail, my next rewatch I'll pay attention and see if that trait is consistent...
More, if there is a home planet loaded with tons of swirly things and you went to vacation there, which one would want to take you in the most and why? Which one would you want interfering with your thoughts to make you act out? The one that feeds off of hate, or happiness, or jealousy, or greed, or people who keep writing the word "shrimp fork" incessantly, or what? Even more fun, if this were a Phase II script, would they all go all disco and strip and jiggy as a result? Inquiring minds don't want to know. But did all these fritters die out because they fought each other and now opted to seek out other life forms and strange new worlds as a warped parody and, indeed, how do these swirly gasbags travel faster than light? There's a difference between some open-endedness and actual vagueness, but let's put all that to the side:
Nice exposition for anyone tuning in at just that precise moment, too. Superb music, applied with care, and a first-rate performance from DeForest Kelley. The story is loaded with terrific set-pieces and acting from all, as well as going quite far for 60s TV, but as this naturally involves the "most disliked", I've still got to put in something dislikedable and nitpickery. (the most-liked, to compare, I'd have to refrain from being nitpickery and just praise it. The story's worth a lot of praise, regardless, nitpicking can be done out of trying to fill in the missing pieces, mentioning something out of disappointment, and a slew of other possible reasons. I mean, "Oi, we're out of anchovy ice cream with gerbil-flavored topping, so now I need to gripe, grrr!!!" is an actual reason used by, at least if not by most, 0.000000000125% of the population, possibly...)
The TOS-R CGI of adding in the Klingon ship with smaller explosions is a very nice touch. Also, at 0:49 in, are those bright pink feathers taken from a burlesque show and plonked into a bit of styrofoam? We've seen the flamingo frills in previous episodes, just not as incessantly as any given episode of "Lost in Space". Which is okay, Trek has reused props before and nobody really cared as much because the scripting was more often really good. Which wouldn't stop people from noticing and, being sci-fi at the time, it was far more costly as sets and props could almost never be reused due to being so iconic. I think "Mork & Mindy" got away with as much as they could, solely because it was 11 years later and had fans other than Trek fans so nobody would notice the modified Col. Green outfit, the spacesuit from "The Tholian Web", the large egg that Cap. Kirk didn't sit on, and so on.
Also, the alien has a neat practical effect, filming water going down a bathtub drain and superimposing it over the live action...
Lastly, Kang realized when he ran out of gerbil:
Amazingly, the swirlie couldn't tell that Kang was faking it and projecting a really hard slap. Now it's a two-parter, whoops! Well, not really, the fritter knew the crystals would be depleted and would then leave and find another host at another hotel anyhow.
)
I'm really not sure what's worse, augmenting the planet's name to recognize the dominant species, or playing "fourth wall phonetics" as "Qo'Nos" is pronounced like "Chronos" and ties not only into all the Shakespeare of TUC, but also that movie's themes of time running out, forging a peace, etc, etc. Given the spelling, I'll go with "Qo'Nos" as "Kling" isn't great and since we're not called "Earthers" or "Earthlings" anymore and our planet isn't called "Humanidity" or anything just as dumb, no - we just call it the same thing we call dirt: "Earth". Hey, that's what we can call people: "Earthworms". 
Well, maybe not... 
