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Slip from the grasp
rogue utility 16

no action

Trigger: your turn starts

Effect: "If you are grabbed, the grab ends. If you are subject to an effect that is slowing or immobilizing you, the effect ends. You can also make a saving throw against an effect you are subject to that a save can end."[HotFL:188]

Slip from the grasp is an encounter power available to rogues at 16th level.