Vanguard's lightning
invoker attack 1
Target: each creature within this power's area of effect
Attack: Wisdom vs. Reflex
Hit: "1d6 + Wisdom modifier lightning damage. Whenever the target makes an opportunity attack before the end of your next turn, the target takes lightning damage equal to your Intelligence modifier.
"Level 21: 2d6 + Wisdom modifier lightning damage."[PH2:103]
Vanguard's lightning is an at-will power available to invokers at 1st level.