A couple changes to the SA form to make it feel better.

P: 12-44% of the damage dealt in your first 3 seconds of combat with champions will be dealt again to those champions as a burst of magic damage at the end of the duration.

Very similar, but its impact in the early game would be more obvious and being one shot without being able to respond would be less common. It's less powerful than the current passive, but would feel miles better to use, since you currently hardly notice it early on.

Q: A shadow spins in your place, removing the action lockout during the cast time.

Just a little thing to make the "slick assassin" feel smoother.