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Choices are quite limited when picking evil companions: we have Korgan, Viconia, Edwin, Dorn and Hexxat in SoA, and Sarevok in Tob. The good news is, together with an arcane protagonist, the five evil npcs already form a balanced party: 3 warriors, 2 mages and 1 cleric.
I don't see any problem also using Cernd and/or Jaheira. And Jan (he has a bit more improved stuff at this point). Then there's simply a reputation patch that you can install (I think I've even added one to IA Tweaks).
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I wonder whether an evil nec protagonist could still collect and equip memory of the apprenti/lord of the underworld (and less importantly, scarlet ioun stone and cloak of arcane immortality). Moreover, is there any way to use Sarevok in SoA, with the help of EEKeeper?
Well, IATweaks does allow access to the new content for other protagonists, so you can try it. But there might be things that I did not account for, since some quests might require a reputation of 20, or something. As for Sarevok, I don't think that's a good idea. I mean, you can probably summon the character but all of his scripting and internals are restricted to ToB.