Call of the beast
druid attack 1
burst 1 within 10 squares
Target: each creature enemy within this power's area of effect[U
:11/2009]
Attack: Wisdom vs. Will
Hit: "The target can't gain combat advantage until the end of your next turn. In addition, on its next turn the target takes psychic damage equal to 5 + your Wisdom modifier when it makes any attack that doesn't include your ally nearest to it as a target.
"Level 21: 10 + Wisdom modifier damage."[PH2:84]
Call of the beast is an at-will power available to druids at 1st level.