The frostleaper's CR should be 2--I have modified the statblock to match.
Next one is inspired, yet again, by a name drop in the Pathfinder Campaign Setting. You'll note that, despite its identical ability scores with an ordinary unicorn, the twilight unicorn is one CR higher. Why? For one, its abilities are somewhat more offense oriented. For another, unicorns are really quite broken for their CR.
Twilight Unicorn
This powerful equine creature has a coat so black it seems to absorb the light around it, and its eyes gleam a sinister red. A single jet-colored horn, about two feet long, grows from the center of its forehead.
Twilight Unicorn CR 4
Always LE Magical Beast
Init +3; Senses darkvision 60 ft, Listen +8, low-light vision, Spot +8
Aura negative energy (10 ft)
Defenses
AC 18, touch 12, flat-footed 15
(-1 size, +3 Dex, +6 natural)
hp 42 (4d10+20)
Fort +11, Ref +9, Will +8
Defensive Abilities hide in plain sight, tomb-tainted; Resist positive energy 10; Vulnerable tomb-tainted
Offense
Spd 60 ft (12 squares)
Melee +3 horn +11 melee (1d8+8) and 2 hooves +6 melee (1d4+2)
Space 10ft; Reach 5ft
Spell-like Abilities (CL 8th)
At will—detect good
3/day—inflict light wounds (DC 18)
1/day—greater teleport (within home forest only), inflict moderate wounds (DC 19), poison (DC 20)
Special Attacks powerful horn
Morale
Before Combat twilight unicorns will shadow intruders for hours or days, using stealth to keep close until they are most vulnerable.
During Combat a twilight unicorn begins combat with a charge, preferably from hiding. During combat they combine powerful melee attacks with their touch spells.
Morale ferocious, but not stupid, twilight unicorns know the value of retreat. If reduced to 10 or fewer hit points, they will either teleport or hide in plain sight, using any remaining inflict spells to heal themselves before plotting revenge.
Statistics
Str 20, Dex 17, Con 21, Int 10, Wis 21, Cha 24
Feats Multiattack, Stealthy
Skills Hide +7, Listen +8, Move Silently +11, Spot +8
Base Attack +4; Grapple +13
Languages Common, Infernal
Ecology
Environment warm forests
Organization solitary, pair or unkindness (3-6)
Treasure none
Advancement 5-8 HD (Large) or by character class
Level Adjustment +4 (cohort)
Special Abilities
Hide in Plain Sight (Su) A twilight unicorn can make a Hide check even if it is being observed, so long as it is within 10 feet of shadowy illumination.
Negative Energy Aura (Su) A twilight unicorn constantly radiates an aura of negative energy. To living creatures, it does nothing more than create mild discomfort (no game effects), but it empowers the undead. The twilight unicorn and any undead creature within the aura gains a +2 bonus on all saving throws (this bonus is included above) and resistance to positive energy 10. The twilight unicorn cannot suppress this effect.
Powerful Horn (Su) The horn of a twilight unicorn acts as a +3 weapon and acts as a lance, dealing 1.5 times the twilight unicorn’s Str modifier and dealing double damage on a successful charge. A twilight unicorn can cast touch spells and hold the charge in its horn. When it gores an opponent when holding a charge, it deals regular damage and the opponent must save against the spell.
Tomb-Tainted (Su) Like an undead creature, a twilight unicorn takes damage from positive energy and is healed by negative energy.
Skills Twilight unicorns gain a +4 racial bonus on all Hide and Move Silently checks.
Twilight unicorns were once powerful creatures of good, but have been warped into beings of darkness and evil by the corruption of Geb. A twilight unicorn typically grows to eight feet long and five feet high at the shoulder. Rather thinner than ordinary unicorns, they weigh 1000 pounds on average.
Ecology
The turn of the nation of Geb to necromancy and undeath made its mark on the very land itself, and twilight unicorns are emblematic of this corruption. No longer valiant defenders of the forests, they gladly allow evil to wander through their glades, but will violently attack those of good spirit. Twilight unicorns are omnivorous, feeding both on negative energy-tainted vegetation and on the flesh of those they kill. They have no natural predators, but plenty of unnatural ones—necromancers seek the blood and horns of twilight unicorns as potent spell components and to craft items associated with negative energy.
Habitat and Society
Twilight unicorns are native to Geb’s Axan Wood, where the only trees that grow are either dead or undead. There, they carve out strict territories amongst themselves—a twilight unicorn will never knowingly impugn on another’s territory without invitation or permission. Twilight unicorns are generally solitary creatures, although mated pairs may share territory. Whispered of in tavern tales in Mechitaur is the Twilight Moot, in which all of the twilight unicorns in the Axan Wood meet to discuss the affairs of the forest and plot the deaths of those who would seek to restore it to health.
Twilight unicorns are on occasion found outside of the Axan Wood. They are less resistant to being ridden than ordinary unicorns, and are less selective of their riders—any evil-aligned master will suit it fine, although they prefer the stability of law to chaos. Ownership of a twilight unicorn is seen as a mark of high status amongst the Umbral Court of Nidal, and they have been successfully introduced to the Uskwood as another layer of security protecting the secretive capital of Pangolias from the scrutiny of the outside world.
Twilight Unicorns and Class Levels
The shadowy stealth of twilight unicorns makes them well-suited for the roguish arts—rogue is a favored class for them. Most twilight unicorns that can cast spells are clerics of Zon-Kuthon, choosing Darkness and Death above his other domains.
The Pathfinder Chronicles Campaign Setting is copyright 2009 Paizo Publishing.