Since Cassiopeia is keeping her APC direction... (Ult suggestion)
I was thinking her ult could be 2 parts,(much like Riven) 1st part is a steroid that gives her Vamp and other bonuses and then the 2nd part is her Petrifying Gaze but with an increased range, no cast time (because they will know you can stun them when you use the 1st part), decreased damage and the stun now increases if they are closer to you (1 to 3 seconds?)