Void Hound, Seeker (CR 3)

Medium Magical Beast (Extraplanar and Void)
Alignment: Always neutral evil
Initiative: +6 (+2 Dex, +4 Improved Initiative); Senses: darkvision 120 ft. and low-light vision

AC: 16 (+2 Dex, +4 natural), touch 12, flat-footed 14
Hit Dice: 3d10+9 (25 hp)
Fort +6, Ref +5, Will +1
Speed: 60 ft.
Space: 5 ft./5 ft.
Base Attack +3; Grapple +7
Attack: Bite +7 melee or slice charge +7 melee
Full Attack: Bite +7 melee plus 2 claw +2 melee or slice charge +7
Damage: Bite 1d10+4, claw 1d6+2, slice charge 1d8+6 plus wounding
Special Attacks/Actions: Slice charge, wounding
Abilities: Str 18, Dex 14, Con 16, Int 4, Wis 10, Cha 6
Special Qualities: evasion, immunity to energy drain, void subtype
Feats: Improved Initiative; Power Attack
Skills: Hide +13 and Move Silently +5
Advancement: 4-9 HD (medium-sized)
Climate/Terrain: Any
Organization: Solitary or pack (1d8)
Treasure/Possessions: None

Source: Web

Immunity to Energy Drain (Ex): Due to their physical makeup, energy drains of any type (level drain, temporary or permanent ability damage, etc.) cannot effect void hounds.

Slice Charge (Ex): A seeker can use its razor-sharp spine as a weapon; to do so, it must charge. The seeker throws its whole body into attack and gains 1-1/2 times its Strength bonus on damage, just as if using a sole natural weapon.

Wounding (Ex): A hit from the seeker's slice charge deals 1 point of Constitution damage from blood loss when it hits a creature. A critical hit does not multiply the Constitution damage. Creatures immune to critical hits (such as plants and constructs) are immune to the Constitution damage dealt by the slice charge.

Skills: A void hound has a +8 racial bonus on Hide checks.

As beings of the Void, the hounds share many of the same special traits as their masters.

Extraplanar Subtype

A subtype applied to any creature when it is on a plane other than its native plane. A creature that travels the planes can gain or lose this subtype as it goes from plane to plane. This book assumes that encounters with creatures take place on the Material Plane, and every creature whose native plane is not the Material Plane has the extraplanar subtype (but would not have when on its home plane). An extraplanar creatures usually has a home plane mentioned in its description. These home planes are taken from the Great Wheel cosmology of the D&D game (see Chapter 5 of the Dungeon Master's Guide). If your campaign uses a different cosmology, you will need to assign different home planes to extraplanar creatures.

Creatures not labeled as extraplanar are natives of the Material Plane, and they gain the extraplanar subtype if they leave the Material Plane. No creature has the extraplanar subtype when it is on a transitive plane; the transitive planes in the D&D cosmology are the Astral Plane, the Ethereal Plane, and the Plane of Shadow.