Walkers are slightly different than all the other species in the Mercy Thompson Universe. We've written up a short summary here, but these are certainly not our creation. A link is provided at the bottom to a website that tracks lore from the Mercy Thompson Universe.
Walkers are not made, like vampires or werewolves, but they also aren't born in true lines like Fae. There are no "half" walkers. Like werewolves, they are shifters, but unlike werewolves they are not two entities in one body, they are simply a person who can assume the form of a single animal. Which animal varies from walker to walker.
All walkers have native North American lineage, and are from North America. Their heritage might be tied to their parents, or grandparents, or even their great grandparents, but all walkers have this. In essence, being a Walker is being tied to the land of North America in a spiritual and physical way. Being a walker does not necessarily or even probably mean that ones children will be walkers. It might skip a generation, or several generations. It might affect one child in a group of siblings and not the others. It is passed down the family line, and are almost always the same animal. The original connection to the animal is said to come from someone coupling with the personification of that animal totem.
Walkers turn into any living animal native to North America. Their shifting process is painless and without pause. A seamless transition from human to animal, the process does leave their clothing behind but lacks the effort and pain a werewolf's shift brings with it. Their shift is entirely magical and has no overbearing factors like a werewolf's does. They wish to shift, and they do.
Walkers can belong to werewolf packs and can be taken as werewolf mates. The packbond and mating bond work the same with them as they do werewolves. They can also become pregnant and carry to term, but cannot give birth to children that are werewolves, their children are always human or walker. They do not have the dominance pull werewolves do, nor do they feel the compulsion to obey an alpha that a wolf would. (Any walker in a pack, however, would generally obey the alpha to keep things smooth in the pack that accepted them.)
Walkers have a couple other abilities that go along with shapeshifting. All walkers can see ghosts, this is what makes vampires hate them and prompted them to be hunted to near extinction by the same, because finding the ghosts that follow a vampire when it's asleep proves to be a particularly easy way to hunt them. Additionally, this means that walkers can also hear, and speak with the dead that they see. Whether doing so is a wise idea however, is entirely up to the situation at hand.
Walkers are also partially-immune to a great deal of magic, but not fully immune. While the pack and mating bonds do affect them, those are always assumed willingly. Fae magic might, or might not work on a walker, the more powerful the fae or artifact being used the more likely it is to work, but even then it will wear off quicker or work less effectively than it would on a human.
Walkers have the same lifespan as humans do. Walkers cannot shift parts of their bodies. It's all or nothing.
Native American Legends featuring animals (Note: Pay attention to the tribe/location of some of these, as Mayan legends are included but are not appropriate for reference.)
List of North American animals *
* Not every animal is available for play. Jaguars, for example are not allowed. They must be animals currently native to North America.
As a note: Walkers cannot turn into wolves. You are free to choose any currently living animal based in North America/Canada. They must be native to North America/Canada. You may not choose extinct animals, Central American or South American animals. Walkers have ties to the Native American tribes and this should be kept in mind when rolling one.