Source: Patreon December 2022 Questions Thread
Let's take a look at Skaravojen. After the near-assassination of a Keeper in 321 YK, High Cardinal Syketel worked with House Vadalis to create a guardian for the Keeper, and they produced Skaravojen: a creature that seems to have some traits of dragon and basilisk (scales, six-legged); who possesses human-level intelligence; fast healing and seeming immortality; absolutely immunity to enchantment; the ability to detect evil and to DISCERN LOCATION—an eighth level spell effect—at will... and, they're absolutely loyal to the Keeper and both Cardinals and Keeper TRUST that loyalty despite Skaravojen's terrifying appearance.
So, first of all we have the fact that there's no way that Vadalis could produce a creature with these capabilities through standard magebreeding. Sentience, fast healing, and enchantment immunity alone would be huge if Vadalis could produce any of them on demand, not to mention being able to Discern Location. It's said that "the secrets of its origin are kept safe by House Vadalis" which I'm sure is true; the biggest secret being "We didn't actually create it" or, if they did, they only created the vessel with was then filled by a divine force.
So in my campaign, High Cardinal Syketel began working with House Vadalis to create a guardian after the near-assassination of Keeper Ghelios. But Skaravojen wasn't actually produced until after the death of Keeper Ghelios and the appointment of the next Keeper. While celebrated as a marvel of House Vadalis, Skaravojen is actually a miracle of the Flame, negotiated by Ghelios, Syketel, and Samyr Kes. What's the secret that allows the Cardinals and Keeper to have such faith in their guardian? The fact that SKARAVOJEN CHANNELS THE SOULS OF THE DEAD KEEPERS. A principle of the Flame is that the souls of the faithful strengthen the Flame after passing through Dolurrh. Well, not the souls of the Keepers; they are channeled directly into Skaravojen, enhancing its celestial power. This ties to its longevity; Skaravojen has actually grown STRONGER over the centuries, because each Keeper adds to its strength. The souls of the Keepers are a passive gestalt within Skaravojen and don't retain any sort of individual consciousness or identity. The Cardinals and the Keeper know this; Jaela knows she'll be bonded with Skaravojen after death. But because they feel most people wouldn't understand, it's a closely held secret.
And that's how you have such a remarkable creature supposedly produced by Vadalis, but they can't produce another. All of the things that make Skaravojen remarkable—sentience, supernatural abilities, longevity—are tied to the power of the Silver Flame and the spirits of the Keepers bound within it; "Vadalis Magebreeding" is just the cover story.