Just wondering...
What determines the strength of a Rare NPC and which artifacts can be used against it?

Case in point...

I can use Drannik Saboteurs and Dark ACFs on the Slithion Queen (level 300), but not on the Sha'Din AI Matrix (level 200), because that one says it's too powerful.

That doesn't make sense to me and mine.

Any ideas, help or suggestions?

Maj

You can't use Sabs or Foci against Boss NPC's and the AI Matrix is a Boss, whereas the Queen isn't.

There are two different kinds of rares...Boss status and Elite status. Elites are 3 or 4 person drops and can have the full range of all 4 (Dark Void Foci, Drannik Sab, EMP Sphere and Disarming Bomb) used against them, whereas Boss status rares are 10+ player rares, and are significantly stronger. Only EMP and Disarming can be used against them, as well as Recondite Intruder can be used on both. Hope this helps