For the second and final time, Star Trek attempts a holiday tie-in with this Halloween special from 1968, unaware that people would see the episode in the ensuing decades at all times of the year, thanks to syndication. Written by the same guy who wrote "What Are Little Girls Made of?", this one is actually more like "The Squire of Gothos" but without the charm. Once again, we have Kirk and company discovering a mysterious castle on a desolate planet where they are toyed with by powerful beings that tap into Earth-history but don't quite get it right. This time, all the old Halloween cliches are pulled out, from skeletons to black cats. (The latter, of course, leads to the episode's cute title. A catspaw is a term derived from The Monkey and the Cat, a fable by Jean de La Fontaine, meaning a person or persons used unwittingly by another to accomplish the other's purpose").
The plot off the episode is loosely based on Bloch's short story, "Broomstick Ride", published in Super Science Fiction magazine in 1957. Unfortunately, it doesn't work well as a Star Trek story. The episode's strong suit is its humor with funny bits such as Spock's summation of a witch's curse ("Very bad poetry") and the sight gag of Kirk, Spock, and McCoy hanging in chains next to a skeleton hung the same way. (As McCoy eyes the skeleton, Kirk says, "Bones?" and then quickly clarifies, "Doc?") Perhaps the funniest moment, however, is an accident. As Antoinette Bower, playing a female alien, attempts to leave her character's throne and approach Shatner, part of her wardrobe becomes caught on the chair and she becomes stuck. Nevertheless, she gamely finishes the scene as if everything is normal! (Actually, there's another silly thing that happens at the top of the episode too. After Kirk requests McCoy's presence in the transporter room, he and Spock exit the bridge to meet the doctor there. Next thing you know, Kirk shows up in the transporter room alone. To fix this problem, the syndicated version cuts out Kirk and Spock's exit from the bridge, but this also cuts out Kirk's request for the doctor. Thus, when McCoy suddenly bursts into the transporter room to join Kirk, it looks like he really isn't just a doctor but a mind-reader too).
Nitpicking Star Trek, of course, is an easy sport. But whereas "Squire of Gothos" has a quirky spirit that makes up for its flaws and ties the plot together, "Catspaw" has no thru-line, being uncertain what it really is. The fundamental problem is the dichotomy of Halloween and Star Trek. The former is about taking delight in the fright of things that go bump in the night, whereas the latter is about being curious and figuring out what's making the bump.
Unfortunately, the problems turn the episode into a waste of Bower ("Sylvia'), one of TOS's most prestigious and talented female guest stars. It's also a sad swan song for Theodore Carroll ("Korob"), who died in a drunk driving accident a few weeks after the episode first aired.
So where else does Star Trek reference a holiday? In "Charlie X" (which was originally supposed to air around the time of Thanksgiving in America), there's a plot point about turkeys that ties into the holiday. (I suppose it's also worth mentioning that TNG's "Pegasus", mentions an annual event called "Captain Picard Day").
Remastered Edition: This gets the basic redo with new shots of the Enterprise in orbit - which are quite well done. Other touches include a new matte painting establishing the castle (with the original shot, only showing the entrance, composited into it), some minor improvements in special effects, and the digital removal of the strings used to control the aliens at the end. They choose not to, however, fix a glaring mistake: the witches that appear near the beginning are overlit, and their black turtleneck shirts are easily visible, ruining the intended "floating heads" effect.