The ranger has an attack that lets you place her on any square of the tile she is in after the attack. Can you still do that if you are immobalized? its part of the attack action.
Until stated otherwise, I say yes. There are a few cards, both Power and Encounter, that would move your character. Slow and immobilized only effect your "Move" action of the Hero phase.
If you had to reconcile it thematically, you could say that by using the Power you are moving your body by sheer will to attack your enemies.