I currently have a Clvl 79 Poison based javazon (complemented by LF and Slvl 1 Jab). and it works!
The main problem with poison it slow kill speed, but there are several overlooked advantages:
1 - fire and forget: launch the 4k damage plague cloud, and retreat, come back few seconds later, repear until done - no risks, collect all the godies
2 - true PMH: I poisoned to 1/2 HP a group of monsters and 10 mins later they did not heal at all (this was in Hell Act3 on Cold imune zombies in Black Marsh). I will try this on an Act boss on NM, just to see how it works.
3 - "Low" mana cost: you have the embedded delay, but you should only cast PJ only about 5-10 seconds or so, and meanwhile re-charge with jab & mana steal!
[edit]: Oh... and one more thing: Normal and NM are a breeze with Plague Javelin... most of the time 1 shot kills all. Hell is a different story, but still PMH is awsome!
4 - works great with any javelin! (no real need for uber gear)
The other problems are Poison imunes, and you should really have some other element to complement this skill with (LF is probably best choice - i got that to Slvl 20 also)
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