The description says all resistances. But when i walk near a conviction aura mob, it only reduces by fire, cold, lightning resistances. Deciding whether to use conviction with a poison nec.

no

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"Silence is golden when you can't think of a good answer",- Ali.

Conviction only lowers resistances of fire, cold and lightning. You need to use Lower Resist curse to lower poison resistance.

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Go and terminate with extreme prejudice
Most people just take steps. I take dubsteps.

so do most poison chars use A3 poison merc?

This is really your choice; if you're a necromancer it's not necessary at all since you have Lower Resist. I believe poison necromancers choose A1 physical merc because it is potentially a very strong alternative damage type to poison, and serves for an easy start to Corpse Explosion spamming.

As for a Rabies druid or a poison amazon, you may want to find either a tank-type mercenary or just go for a different type of damage. I'd personally go for the latter--one type of damage isn't that great in hell.

If you're looking for other means of -poison res, you can find it on equipment, easiest to find on necromancer gear even.

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-ISO- Moonstone Rubies, +6/-6 Psn/Lite Facets,
Hearts (pal/nec/dru/zon), Braaaains

Then how would the A1 merc synergize with a poison nec? Or its more of just getting 2 damage types with no synergies involved? Since most of the time u'll be casting LR rather den amp/decrepify. The only synergy i can imagine would be casting LR, poison dagger, decrepify and let A1 merc hit. Rinse and repeat..

Also, anyway to break magic immunities? And any particular gear/runeword/merc dedicated to -magic resistances?

For rabies.

A1 merc - uniq xbow to cast LR on mobs.
A3 or A5 merc - once they are lvl86 and can use Medusa's as a source of ctc Lower Resist.

The hit and run aspect of rabies makes an A3 merc kinda mediocre as they tend to be left in the middle of a mob and die. (at least that was my experience). My A1 merc was much sharper and avoided death easier. Could have been the addition of life leech too.

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People who live in cinder block houses can throw whatever they want.

A3 mercs are fantastic if equipped right throughout the game. Load up with life regen until they are 55, then fill a shield with skulls for them at 88 to help max dr%. a little life per kill after that will make them sturdy, I've used an act 3 merc for pretty much every build this ladder since i refuse to use a1 mercs. Light mercs clear trash at an insane rate and the AoE of charged bolt and chain light is better than multishot IMO. make sure once they hit 55ish they have 140%+ fcr at all times and as much passive pierce as possible.

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