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Stalker's strike
shaman attack 1

Target: one creature

Attack: Wisdom vs. Fortitude
If the target is bloodied, the attack roll gains a bonus equal to one-half the user's Intelligence modifier.

Hit: "1d10 + Wisdom modifier damage. Until the end of your next turn, your spirit companion can flank with you and your allies."
Level 21: "2d10 + Wisdom modifier damage."[PH2:121]

Stalker's strike is an at-will power granted to shamans who select the Stalker Spirit option for the Companion Spirit class feature at 1st level.