Well, since I've never played a poisonmancer I don't have much to contribute. But I am on USEast Ladder softcore and have Death's Web and full TO (I just switched my mancer from TO to MF gear) for trade on my
list if you're looking for them.
As for boss killing, my full summoner uses an HF merc (as suggested above) and him + Gumby + Decrep does wonders. If I fight Baal, I normally don't lose a single minion (except Revives). In fact HF + Gumby slows so much by themselves sometimes I don't even bother with Decrep and I use Amp instead to increase the killing speed. Giving him a Kelpie Snare or something similar would slow him even further.
And one other piece of advice, if your main problem is boss killing, try putting some Crushing Blow on your merc. I have just switched and given mine Guillam's and Hone Sundan. Once I get a -15 req / +24% ED jewel I'm trading for I'm going to upgrade the Hone Sundan and put 2 Shael in the other 2 slots. Not sure what to socket the armour or helm with yet, probably Shael or ED jewels since he doesn't really need to leech much. Oh, and he's wearing an upgraded Shaftstop for armour but I may switch that for an upgraded Duriels or a Gladiator's Bane or something with +skills, not sure yet. I haven't tried the new gear yet, but the CB should make boss killing much quicker. And since the army does most of the work for me, he doesn't have to be a massive tank, for you upgraded Shaftstop would probably be the best for the DR% and high defense.
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Darzog