[@Romero]

Hmm... Just an idea if we're suggesting traits...

Raise undead monsters– Through hunting or farming, you managed to slaughter and raise a monster from the dead as a mount. Be it giant spiders, wargs, big boars or any other monstrosity that roams your lands, they now serve you in undeath. These undead creatures are fast and loyal as well as extremely savage. (Light Cavalry gets an advantage)

Raise undead mythological monsters– (Requires Raise undead monsters) Creatures of myth can now be raised from the dead. These things were more than simple monsters in live. Such beasts as Erymanthian Boar, a Manticore or a Direwolf can now be killed and brought back from the grave. Far stronger in combat and undyingly loyal to their necromancer master, the undead beasts of lore will destroy any fool who stand in their way. (Heavy cavalry gets an advantage)

On undead wings I fly! – (Requires Raise undead mythological monsters) Though mastery of necromancy and the skills of your people, you can now raise flying beasts into undeath. Maybe it was a gryphon, or a wyvern. It doesn’t matter. What does are the vicious claws that are now at your disposal in the skies. (You can make Aerial Interceptors and Fasts without requiring the Dirigibles trait)