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Storm spike
druid attack 1

Target: one creature

Attack: Wisdom vs. Reflex

Hit: "1d8 + Wisdom modifier lightning damage. If the target doesn't move at least 2 squares on its next turn, it takes lightning damage equal to your Wisdom modifier.
"Level 21: 2d8 + Wisdom modifier damage."[PH2:85]

Storm spike is an at-will power available to druids at 1st level.