Quite a relevant question. Mercenary survivability and survival, in short. Primarily in the form of damage reduction combined with resistances, so stuff like the iron pelt would be ideal. For that reason Mephisto is both the best and the worst. He can drop almost everything of interest in this regard but the way to him is littered with fire spells, chiefly the hydras, that are very risky for mercenaries. Without teleportation it will be tedious to fight through, and tedious is always dangerous.
Actually, it's maybe even a little early to contemplate magic finding for they have to make it through nightmare Act II first and also obtain some decent magic finding gear in the first place. I think I'll skip hunting for more Sol runes, it's too boring and Octavia, who would need them most, doesn't have any decent socketed plate or helm to put them in yet.
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