Requirement: The user's spirit companion must not already be present.[U:10/2010]
Effect: "You conjure your spirit companion in an unoccupied square in the burst. The spirit lasts until you fall unconscious or until you dismiss it as a minor action. The spirit occupies 1 square. Enemies cannot move through its space, but allies can. When you take a move action, you can also move the spirit a number of squares equal to your speed.
"The spirit can be targeted by melee or ranged attacks, although it lacks hit points. If a single melee or ranged attack deals damage to the spirit equal to 10 + one-half your level or higher, the spirit disappears, and you take damage equal to 5 + one-half your level. Otherwise, the spirit is unaffected by the attack."[PH2:120]
The March 2010 update added an additional condition to the spirit companion's duration such that it expired if call spirit companion was used again. That change prevented multiple spirit companions from being summoned. The October 2010 update then reverted that change, and replaced it with a requirement that the spirit companion cannot already be present. That change still prevented multiple spirit companions from being summoned, and also prevented shamans from dismissing and resummoning the spirit companion in one minor action.
Powers based on the spirit companion have the spirit keyword. These powers can only be used when the spirit companion is called, and unlike regular conjurations, has line of sight and line of effect from the spirit companion's space, which is also the power's origin square. [PH2:220]