These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Old Kingdom
Complete Monster: After Kerrigor aka Prince Rogirek became one of the Greater Dead, he tricked his half-brother into helping him murder their mother and their sisters in order for Kerrigor to use their blood to shatter the Charter Stones protecting the kingdom from the dead. Defeated and driven deep into death, Kerrigor's actions nevertheless destroyed The Old Kingdom, allowing all manner of The Undead free access to the world over the next several hundred years, while he waited for the chance to break free. Kidnapping the infant Sabriel, Kerrigor took her deep into death as part of a plot to blackmail her father, The Abhorsen, into freeing him. Years later, he traps The Abhorsen himself in Death and breaks free into the world of the living. He then tries to capture Sabriel and his revived half-brother as part of a plan to shatter the remaining Charter Stones. When this fails after The Abhorsen's Heroic Sacrifice, Kerrigor re-emerges from Death and leads a massive army of undead across the wall and into a girl's school, killing soldiers and students alike, before devouring Sabriel's Friendly Enemy, Mogget, alive and finally forcing Sabriel herself into a Mutual Kill. Obsessed with power and staying alive no matter what the cost to others, Kerrigor is the worst that the realm of the Dead has to offer.
Magnificent Bastard: Depending on either your opinion of Mogget, or where you are in the series. Mogget does get better, mostly over the course of the third book. But even though Mogget can be quite caustic when he is criticizing the plans and plots of several characters, or griping about his slavery or the incompetency of his keepers, he both does his part when crisis strikes and sometimes does things that are not required of him. And at the very end, when those who are standing in for the original Seven are just about to falter, Mogget steps in and adds his power to the binding and helps to save the world.