Turn your mount into a mummy lord
Considering that the Mummy Lord template was originally created for humanoid creatures, but actually has no restriction on creature type, there are quite a few advantages on applying that template to your mount:
- It gains a lot of strength (+8) and hit points (+6 to charisma and toughness);
- It gains a breath weapon;
- It can try to control other undead (including your team mates, mind you);
- Its attack has a powerful curse;
And the best part, it will automatically rejuvenate within 1d10 days if completely destroyed.
The largest drawback is the despair aura, which must be saved against at least once per day and there is nothing that prevents this other than becoming immune to fear and/or mind-affecting effects. Once afflicted, you are immune to this aura for 24 hours.
Unlike many other templates (such as zombie lord, juju zombie or skeletal champion), this template actually has a price attached to it (similar to lichdom):
“Mummy lord” is an acquired template that can be added to any living corporeal creature (referred to hereafter as the base creature) that has at least 8 Hit Dice. The process of creating a mummy lord requires 50,000 gp worth of rare herbs, oils, and other mummification materials. The mummy lord retains all of the base creature’s statistics and special abilities, except as listed below.
Bear in mind that, unlike druids who must pick animals as their companion, the Nature mystery's power (Bonded Mount) has no such restriction, similar to a cavalier's mount instead. So, unlike a druid (see Nature Bond), who would be forced to retrain into an archetype that allows creatures with the undead type as companion, you simply have to use one of the listed animals for your creature's size, a horse or camel for a medium-sized oracle, or pony, dog, wolf or boar for small-sized oracles. There is no restriction saying that your horse cannot be an undead horse.
For a cheaper alternative, you could look into the Mummified Creature template, which, while not as powerful as a template, is much easier to apply to your mount:
To create a mummified creature, a corpse must be prepared through embalming, with its internal organs replaced with dried herbs and flowers and its dead skin preserved through the application of sacred oils. Unlike with standard mummies, a mummified creature’s brain is not removed from its skull after death. Injected with strange chemicals and tattooed with mystical hieroglyphs, a mummified creature’s brain retains the base creature’s mind and abilities, though the process does result in the loss of some mental faculties. Once this process is complete, the body is wrapped in special purified linens marked with hieroglyphs that grant the mummified creature its new abilities (as well as its weakness). Finally, the creator must cast a create greater undead spell to give the mummified creature its unlife.
Note that Create Greater Undead should be available at 11th level, and the template simply expands the possibilities of the spell, which already includes the possibility of creating juju zombies and skeletal champions, as mentioned earlier.