If someone casts 3 or more voodoo curses on me, I can utilize the "Avenge" ability when hitting back. Can I also use that if someone tried to cast voodoo on me 3 or more times, even if only 1 or 2 got through my mindbar?

Say, for instance, that I have a mindbar, and someone casts 3 Spy Networks on me. The first 2 fail, but the last one succeed. If I return fire, will my voodoo get the "Avenge" ability, or does it have to be 3 SUCCESSFUL voodoo casts for that to work?

I think it is successful casts.

it's only castings it doesn't need to be succssesfull if my memory serves me right

Well we can find out.

Works with blocked and live casts.