Tradition Book: Euthanatos is interesting because it goes in the exact opposite direction as all the other revised Tradition Books. Instead of exploring more and more abstract death magic, it's actually about this specific weird group of guys with their own specific weird set of beliefs. They aren't the Indian mages. They aren't even the Hindu mages (that's the Celestial Chorus - hilariously making the Chorus represent most of the world's organized religions). They are a heretical cult that thinks they can heal the world by killing a sufficient number of assholes. It attempts to fulfill Mage Revised's globalist mandate by giving them a complex, idiosyncratic history. The Pomegranate Deme don't represent the Eleusinian mysteries, the Madzimbabwe ghost-summoners aren't the official religion of the historical Great Zimbabwe, and the Aided bear only the thinnest connection to Celtic mysticism. They're in an alliance with India's Charkravanti because 800 years ago, the mystic Sirdar Rustam went on an epic road trip, and they were the oddball death-worshipers that he just happened to find.
In a way, Mage does a disservice to the Euthanatos by making them a full Tradition. What they really need to be is small and insular, an esoteric order that gets really into its own peculiar theology. They believe that "purity and cruelty aren't necessarily opposites" and that "the Wheel [of karma] is beautiful, why go to all the trouble to escape it" and holy shit, they would absolutely be the dangerous cult you'd try to stop in a more reasonable game. But here, they're one of the big nine PC groups, so the book is kind of obligated to try and make them into protagonist material.
I'm not sure if it succeeds, but it does manage to be pretty challenging along the way. It accomplishes this through a framing fiction that I'm going to need to attach a content warning to (for child abuse and rape).
So, in the opening fiction, our viewpoint mages are in the process of delivering vigilante justice to a pedophile serial-killer and in the middle of their assassination, they discover that he has a wife. It's unclear the precise degree of her complicity, but she is definitely an accessory to his crimes. She's the one who keeps them fed while they're in the dungeon and she's the one who buries the bodies afterwards. Though the Euthanatos rescue some of the victims alive, by the time they get there, the kill count is at least 20. They dispatch the killer, but "she's salvageable."
It's interesting to me that the most morally fraught decision in Tradition Book: Euthanatos is an act of mercy. It's a pretty canny artistic choice, because it changes the framing of the discussion from "are they allowed to kill" to "are they allowed to unilaterally dispense justice?" There's a bit where the Celestial Chorus tries to use Mind magic to get Janine to turn herself in to the authorities, and the Euthanatos characters treat this like it's some kind of profound dick move, but it really is highly uncomfortable that she ends the book breathing free air. The fact that she did what she did because she feared for her life may matter for her karma, but I'm not sure her victims will rest any easier knowing that she's been conscripted into a cult of fate-shifting assassins.
There's a line here that sums up the Euthanatos pretty well - "They feared him because he would do the things no angel would do, and because, maybe, just maybe, he spoke with the voice of the true God." More than any other theme or aesthetic, it's this ethical hubris that ties the Tradition together. It's the book's best quality, and it forces us to consider the Euthanatos seriously, but it's another example of one of these Tradition Books stumbling on to something that should be a general theme for all mages and trying to make it the specific property of a particular book. Does being able to tell infallibly the difference between the guilty and the innocent or between those who can be redeemed and those who can't somehow entitle you to make life and death decisions entirely on your own? Does it impose upon you the responsibility to do so?
The other interesting thing this book does is take the corruption of the Euthanatos a lot more seriously. The introduction says it best, "some portrayals of the Euthanatoi have been unbelievably grim and other have been apologist to a fault," but Tradition Book: Euthanatos actually puts in a good effort towards making them human. The metaphysical taint of Jhor Resonance is invoked a little too often, but the book does talk about how their ideal of pure justice is unattainable. The Euthanatos are rarely dispassionate in their assassinations. Sometimes they feel a righteous anger. Sometimes they enjoy their work just a little too much. Both can lead to Jhor.
"In all that pain and sin, in every act that kept us from being what you'd call good or just, we worked toward one fate - in the service of God."
Tradition Book: Euthanatos is in the running for "Revised book that most improved its subject matter," but I'm not sure it successfully makes the argument for the Euthanatos as a Tradition. In addition to them still being, you know, problematic as hell, there's also the small matter of magical style. They are all over the place. The section on foci basically just lists every major category of occult practice. You'd think the death-mages would be among the last of the Traditions to practice ritual sex magic, but you'd be wrong. I shudder to think about it. Then you've got groups like the Golden Chalice, which more or less canonically just practices Hermetic occultism, and you realize that the Euthanatos aren't organized around a paradigm, but rather around a goal.
That probably makes them the most realistic occult society in the Mage: the Ascension universe, but it takes the already confusing question of "what, exactly, is a Tradition" and makes it utterly intractable. On the other hand, they are one of the top three Traditions most likely to survive my "fuck it, the Council is made of Crafts" setting-hack more or less intact.
Ukss Contribution: There's a section, called "Legends of the Euthanatos," that clearly exists purely to drop plot hooks. One is about a conspiracy theory that "the Good Death was meant to engineer a messiah" by ensuring that certain powerful Avatars "coalesce into an apocalyptic god." This seems to me to be a good wrinkle to add to Hyborea's Avatar cult and the sort of background threat that can pop up again and again in the PCs' adventures.