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".