"if you have imp ambush and time it right you could shadowstep behnd something(or someone), ambushx5, backstabx5, bam dead =x"
Then what? Vanish and repeat in 25seconds?

This sounds like AP+POM+Pyro to me. Devastating, but on a timer. It'd be a shortish timer compared to 3min, but not something that would be an i-win button in Arena...