White wolves
Bard Attack 23
You lament the lives lost to the white wolves. So stirring is your song that it draws the howling pack from the spirit world.
Target: each enemy in the blast
Attack: Charisma vs. Fortitude
Hit: 2[W] + Charisma modifier cold damage, and the target falls prone.
Effect: The blast creates a zone that lasts until the end of your next turn. Any enemy that ends its turn in the zone takes 5 cold damage, and it is immobilized until the end of its next turn.
White Wolves is an encounter power available to bards at the 23rd level.[Dr396:31]
This is rated as an excellent choice. It is a combination of a weapon attack against fortitude, knocking targets prone, and forcing enemies to move (risking Opportunity attack or other effects) or become immobilized.