Spirit beast

Spirit beasts are the embodied spirits of the natural world.

In the RPG
They are naturally incorporeal, but may take a true physical form to fight for the druid or shaman who called them. Fighting a spirit beast is harrowing, as the creature phases in and out of existence, rarely appearing in the same place twice during battle. Spirit beasts appear like regular animals, but bear glowing auras and are slightly translucent, even when visible.

Notable

 * ( Added in patch 4.2.0 )
 * ( Added in patch 3.3.0 )
 * ( Added in patch 4.2.0 )
 * ( Added in patch 5.2.0 )
 * ( Made tamable in patch 9.0.1 )
 * ( Added in Patch 7.2.0 )
 * ( Added in patch 3.1.0 )
 * ( Added in patch 5.2.0 )
 * (Thorim's pet, tameable via quest line as of patch 8.1.5.)
 * ( Added in patch 5.2.0 )
 * ( Added in patch 7.1.5 )
 * ( Added in Patch 7.2.0 )
 * ( Added in patch 4.2.0 )
 * ( Added in patch 3.2.0 )
 * ( Added in patch 7.1.5 )
 * ( Added in Patch 7.2.0 )
 * ( Added in patch 4.2.0 )
 * ( Added in patch 3.2.0 )
 * ( Added in patch 3.2.0 )
 * ( Added in patch 3.2.0 )
 * ( Added in patch 3.2.0 )

Speculation
The following creatures are believed to be spirit beasts:
 * Because there is so little known about spirit beasts, it's possible that they could be either:
 * 1) Some sort of demi-Wild God. (Har'koa's mate, Loque'nahak is a spirit beast although not considered a Wild God himself.)
 * 2) Or perhaps the child of a Wild God due to them being relatively powerful spirits that can manifest in the plane of the living just like Wild Gods do.
 * ( Added patch 4.2.0 ) (Tyrande's companion, untameable)

Types of spirit beasts

 * Dire wolf
 * Grimtotem Spirit Wolf
 * Spirit wolf
 * Shadow wolf
 * Spirit pigs (boars, dire boars)

As a hunter pet
Spirit beasts are a rare class of creatures found throughout the regions of Azeroth. Not much is really known about them although more tend to be discovered as the adventurers travel to new regions. Only Beast Mastery Hunters with the level 65 ability Exotic Beasts can tame and summon these exotic beasts.