Use chill touch on most people. I only used numbing on clouds/felar/frost. Numbing is also good when walking around if you're desperate for mvs - it doesn't do NEARLY as much mv bump as Vamp does hp bump, but its helpful.

Honestly, I'd consider playing an arial. The amount of times i died, even as a pretty prepared/competent player, to a trip at the wrong time were just frustrating, even if low.

What i'd do first with assassins (assuming you're not getting lagged out, and have atleast shield up), is consider their race. For drow/halfies, go crimson/poison first. For humans, consider doing weaken or curse first. If you have an army atall (even merc + golem), consider just trying to damage them.

Happy to give more thoughts if you want (here or msg me directly)