My next 101 Series release (coming in april) will be 101 Variant Monsters (PFRPG).
This will be similar to what Archetypes do for existing pathfinder classes, rather than being templates that add things and increase a creatures CR these exchange existing a abilities,
I also using an idea called the Rules of the Rabbit which I originally found in the 2nd edition boxed set called Elminster's Ecologies (I believe this bit was written by Rick Swan) that I use to influence changes in a creature's physical description, its motivations and its behavior patterns.
Here is a quick summary of the rules of the rabbit.
A rabbit isn't always a rabbit.
A rabbit doesn't want to be rich.
A rabbit doesn't always stay put.
Here is what I did with a variant unicorn based on Persian mytholgoy.
Description This vicious carnivores thin gazelle-like creature is as tall as a horse with a single fluted, hollow horn; it has dark patches around its eyes, which make it appear as if it is weeping. A shadhavar moves with exceptional poise though its eyes seem to convey a deep sorrow however this is an utter lie, as shadhavar are cruel creatures who take the greatest pleasure in slaughtering the pure innocence of youth, watching them smile as it murders them.
Alignment CE this replaces a unicorn’s CG alignment
Aura magic circle against good this replaces a unicorn’s magic circle against evil
Horn Song (Su): The shadhavar can choose to cause wind to pass through its fluted horn causing it to emanate a magical melody that attract living creatures within 100 feet and compel them to come toward it unless they succeed at a Will saving throw (DC 21). Affected creatures feel elated and pleased to be near the shadhavar and desire to touch it. The compulsion to stay in the area or touch the shadhavar is overpowering, and victims will fight to follow their urges. Those affected will neither harm the shadhavar nor defend themselves against its attacks. If an unaffected creature spends a full round shaking an affected one, the victim can attempt another saving throw. This can only be attempted once. A successful second save releases the creature from the compulsion, but it can be subject to the effect again as soon as 1d6 minutes later, even if it is no longer within the shadhavar’s range (unless the subject knows for certain the shadhavar is dead). In such a case, the creature must make a third save. If this save fails, the affected creature attempts to return to the shadhavar. The compulsion lasts up to an hour. The save DC is Charisma based.
This replaces all of a unicorn’s wild empathy and spell-like abilities.
Magical Strike (Ex) A unicorn's gore attack is treated as a magic evil weapon for the purposes of damage reduction.
This replaces a unicorn’s normal magic strike ability.
Racial Modifiers +3 Survival in plains this replaces the unicorn’s +3 Survival in forests.
Environment temperate or warm plains this replaces a unicorn’s temperate forests.