Darkenbeast (CR 4)

Medium Magical Beast
Alignment: Always neutral evil
Initiative: +6 (+2 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., low-light vision, Listen +2, and Spot +2

AC: 15 (+2 Dex, +3 natural), touch 12, flat-footed 13
Hit Dice: 5d10+15 (42 hp)
Fort +9, Ref +6, Will +1
Speed: 5 ft., fly 40 ft. (poor)
Space: 5 ft./5 ft.
Base Attack +5; Grapple +8
Attack: 2 claws +8 melee, bite 3 melee
Full Attack: 2 claws +8 melee, bite 3 melee
Damage: Claws 1d4+3, bite 1d6+1
Special Attacks/Actions: Spell imprinting
Abilities: Str 16, Dex 15, Con 16, Int 5, Wis 11, Cha 4
Special Qualities: Immunities, light vulnerability, SR 15
Feats: Great Fortitude; Improved Initiative
Skills: Hide +4, Listen +2, Move Silently +4, and Spot +2
Advancement: -
Climate/Terrain: Any land
Organization: Solitary, pair, or flight (3-4)
Treasure/Possessions: None

Source: Monster Compendium: Monsters of Faerûn

Spell Imprinting (Su): When a darkenbeast is created, its caster can cast a spell that the darkenbeast carries until the spell is needed. On the darkenbeast's master's action, as a spell-like ability, the master may attempt to cast a single spell imprinted on a darkenbeast within 30 feet of her as if she were casting it normally. The spell has a 25% spell failure chance, with an additional +10% failure chance for every other darkenbeast-imprinted spell the spellcaster has attempted to cast that day. Whether the spell succeeds or fails, the darkenbeast immediately dies in a spout of magical purple flame, reverting to its true form in death.

Immunities (Ex): Darkenbeasts are immune to mind-influencing effects.

Light Vulnerability (Ex): When exposed to sunlight, or to light equivalent to a daylight spell, darkenbeasts suffer a -2 morale penalty on all attacks, saves, checks and damage rolls.

Darkenbeasts fight from the air, diving on foes using the charge action for their first attack, then slashing with their talons and biting. Darkenbeasts' primary combat "ability" is enough toughness to soak up a great deal of damage that would otherwise be inflicted upon their masters. Even if they are carrying a truly valuable spell, they tend to fight as if they were expendable. Spellcasters who wish to take advantage of a darkenbeast's imprinted spell often have to call them out of a hopeless melee.