It seems necro dirty pole decay stack with ngahundi decay and it will speed up the decay process.
See this video: https://www.youtube.com/watch?v=BP9ELvAwh5s
How do you think about that? if that can be stacked by using dirty pole + ngahundi combo, all monster will be dead in 10 second regardless of their HP.
So it good to make this build: wiz c3 > link c2 > necro c1 > FF c1. Necro also has soggoth to act as meat shield, and it also can decay too.