Void Hound, Stalker (CR 8)

Large Magical Beast (Extraplanar and Void)
Alignment: Always neutral evil
Initiative: +5 (+1 Dex, +4 Improved Initiative); Senses: darkvision 120 ft. and low-light vision


AC: 16 (-1 size, +1 Dex, +6 natural), touch 10, flat-footed 15
Hit Dice: 10d10+50 (105 hp)
Fort +12, Ref +8, Will +3
Speed: 60 ft.
Space: 10 ft./5 ft.
Base Attack +10; Grapple +22
Attack: Bite +17 melee or slice charge +17
Full Attack: Bite +17 melee plus 2 claws +15 melee or slice charge +17 melee
Damage: Bite 2d8+8, claws 2d6+4, slice charge 2d6+12 plus wounding
Special Attacks/Actions: Slice charge, wounding
Abilities: Str 26, Dex 12, Con 20, Int 4, Wis 10, Cha 6
Special Qualities: evasion, immunity to energy drain, void subtype
Feats: Improved Initiative; Improved Natural Attack (claw); Multiattack; Power Attack
Skills: Hide +8 and Move Silently +11
Advancement: 11-15 HD (Large)
Climate/Terrain: Any
Organization: Solitary or pack (1d8)
Treasure/Possessions: None

Source: Web

Stalkers are simply Large seeker void hounds. They have the following change to their combat profile:

Wounding (Ex): A hit from the stalker's slice charge deals 1d2 points 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.

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.