Invisible Stalker (CR 7)

Large Elemental (Air and Extraplanar)
Alignment: Usually neutral
Initiative: +8 (+4 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., Listen +13, and Spot +13
Languages: speaks only Auran but can understand Common

AC: 17 (-1 size, +4 Dex, +4 natural), touch 13, flat-footed 13
Hit Dice: 8d8+16 (52 hp)
Fort +4, Ref +10, Will +4
Speed: 30 ft., fly 30 ft. (perfect)
Space: 10 ft./10 ft.
Base Attack +6; Grapple +14
Attack: Slam +10 melee
Full Attack: 2 Slams +10 melee
Damage: Slam 2d6+6
Special Attacks/Actions: -
Abilities: Str 18, Dex 19, Con 14, Int 14, Wis 15, Cha 11
Special Qualities: Elemental, natural invisibility, improved tracking
Feats: Combat Reflexes; Improved Initiative; Weapon Focus (slam)
Skills: Listen +13, Move Silently +15, Search +13, Spot +13, and Survival +2 (+4 following tracks)
Advancement: 9-12 HD (Large); 13-24 HD (Huge)
Climate/Terrain: Elemental Plane of Air
Organization: Solitary
Treasure/Possessions: None

Source: Monster Manual

Invisible stalkers can be killed only when on the Elemental Plane of Air. When performing tasks elsewhere they automatically return to their home plane when they suffer sufficient damage to destroy them.

Natural Invisibility (Su): This ability is constant, allowing the stalker to remain invisible even when attacking. This ability is inherent and not subject to the invisibility purge spell.

Improved Tracking (Ex): Invisible stalkers are consummate trackers and make Spot checks instead of the usual Survival checks to trace a creature's passage.

An invisible stalker attacks by using the air itself as a weapon. It creates sudden, intense vortex of wind that pounds a single target on the same plane as the creature.

Air Subtype

This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane Air. Air creatures always have fly speeds and usually have perfect maneuverability (see the section on Movement).

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.