When he's half hp charge at him.
Laser to make him red, a little animation-cancel walk, and the imba range of missile ensures a kill.
Before you missile, make sure to have a good angle so that the fog won't make you miss.
And don't do too much skills during harassing or else he will be red then return to base without you having any skills to finish him off.
Or when theyre in front of you,do first then when they run then that's the time you (in order) use the other razes.
First one is melee range
Second is about a ranged hero's range
Third is about from your Druid of the Talon to the enemies Necromancer/vice versa.