The theme is Monster Manipulation, and that is certainly what you'll get in this hold, along with a strong dose of lynchpin-based rooms that range from not-too-bad to puzzles you may spend hours on.
The main focus is manipulation of basic roaches and other monsters with the 'beeline' movement type, both brained and unbrained. In fact, the best part of the hold for me was seeing how many varied and legitimately interesting rooms could be made with just a few of the basic DROD monster. This goes especially for the trapdoor-path rooms found past the blue gates, which I typically find somewhat tiresome, but ended up all being enjoyable here. There are puzzles based around manipulating brain paths, getting monsters to pressure plates, keeping monsters on/off them, a few minor movement order puzzles, and more. I would definitely recommend it, especially to veterans looking for some satisfying - if difficult - puzzles. However, if you want to try this and you're relatively new, I would also recommend checking out the Simple Sword Tricks and Brained Roach Movement sections of Advanced Concepts beforehand if you haven't, because the information within are the sorts of things you'll probably need to figure out a good number of the room strategies.
There are a few other rooms that require some knowledge of other monsters, but none of those require such exhaustive knowledge as you will with roaches (and I'm reasonably certain that the one room with a snake can be completed without knowledge of their movement patterns).
Before I go though, I thought it was amusing that (Minor Spoilers)
Click here to view the secret text
×the puppet master was easier to kill than his apprentice. At least, I was able to use essentially the same strategy the second time.
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aka VioletPumpkin