Beasts: I used to tell my little sister monster stories when she was naughty. I still have the books, they never knifed anyone and stole their wallet.
Princesses of Diamonds have this to say regarding Princesses of Swords:
Diamonds on Swords: When you need a grand, dramatic gesture, call for them. When you need subtlety, call for someone- anybody - else.
One of the Umbrae, Infectious Hate, allows its user to turn any regular mortal into a Darkened just by delivering them a Breaking Speech. This in itself isn't particularly funny, but the description mentions that every Princess who knows of this Umbrae agrees that it has one positive side. Said positive side? "It's rare."
Another Umbra, Hunger Means Nothing, allow Creatures of the Darkness to survive without having to feed or drink. It however has the side effect of making them lose weight, become physically weaker, and, as described by the book, "look too thin, like a cancer patient, or (some cynical Princesses might remark) a top fashion model."
Instead of having a Practical Magic, Princesses of Mirrors get the ability to have their Transformed form as their default mode, while their mundane form is the one they need to make a transformation roll for. The justification for this? They are so self-absorbed that it is harder for them to be "normal". A Princess of Mirrors is literally capable of maintaining her transformed state through the sheer force of her ego.
The Royal Tongue is frequently mocked for being overcomplicated Purple Prose, making it impractical and hard to use even for a simple sentence. People actually went to ask some of the Queens how such a language came to be. The Queen of Hearts implied it was deliberate, the Queen of Spades burst into laughter, and the Queen of Diamonds (who is fluent in, and prefer, most Earthly languages) gave a put upon sigh.
The Through the Looking Glass Charm allows a Princess to enter the world behind any mirror. One of the advantages this provide is that she can carve out an invisible hole to hide things inside. According to the description, this is "perfect for storing weapons, valuable Bequests or bringing boyfriends you don't want your mother to know about."
The game's wiki provides a page dedicated to crossovers, explaining in details how Princesses interact with other supernaturals. Demons get both a short and long answers. The short answer? "They don't get along".
Then we get the long answer, which basically explains Princesses are creeped out by Demons occasionally becoming stalkish toward them...
Further going along with the Crossovers example is with the Beasts. The opening line?
Princess Crossovers on Beasts: "Of all the creatures of night, Beasts hold the dubious distinction of being the one kind Princesses might like even less than Demons."
The Dream version has a gem when talking about Sworn and their Practical Magic.
"Sworn also have access to their Queen's practical magic (and yes, the Court of Mirrors offers no useful practical magic to it's Sworn)."
Made even funnier in a latter update, where Sworns were given unique Practical Magics to be more useful. Most of them gain ability improving their own abilities, which is actually useful to them. Sworns of Mirrors... get the ability to boost the Princesses they swore to.
An update introduced the "Rising Darkness" mechanic, an optional rule allowing to measure through "Tension" how influent and powerful the Darkness is in the city where your campaign take place. Tension level 2 has this description:
Some conversation on the Discord came up with a funny idea involving a Princess of Mirrors and the Skinchange Charm. It had been confirmed earlier that the Skinchange charm could involve shapeshifting into extinct animals, and combined with Mirror's Practical Magic to stay transformed as an animal indefinitely. Imagine, if you will, a normal Noble of Mirrors turning into a 40ft long, 20 feet tall Tyrannosaurus Rex and being able to stay that way indefinitely.
The Living Image Charm in both versions allows for making a piece of artwork (be it any kind of drawing, dancing, composing, magical confections, fireworks, etc) to hold a charm and release it upon someone who looks at it. There are some upgrades that allow affecting certain people, but in the Dream Version there's an Upgrade involving Tempesta that allows targeting Creatures of Darkness. Naturally, this means the artwork would usually be used to kill them. The text for it speaks best.
"And yes, with the right Charm it is indeed possible to create artwork that makes Darkspawn feel so bad they explode. After all, emotions are magic."