Wok
Member
I think people mostly build Diffusal on her for the mana burn from the illusions. Not sure if it is worth it with how long her illusions are around.
Burning mana is always good in 1 vs 1: Storm Spirit cannot escape, Invoker cannot go invisible or use his spells, Void cannot ult', etc. It usually makes haunting more effective, on top of the slow to get fleeing ennemies. Plus more damage to kill faster and escape quickly.