Pretty much what Mephasm is made of. He never lies, he never fails to be anything less than absolutely polite, and he tries to give the party every advantage and help that he can, regardless of his circumstances. It's generally accepted that he's a Manipulative Bastard, and the most evil figure in the game, despite him never doing a single thing to justify it — in fact, it just makes him all the more magnificent. Cue fan complaints when he never shows up in the sequels.
Shandra's whole motivation for always following you around in Act II — the game doesn't let you leave her behind! — is because bad things tend to happen to her if she doesn't stick very closely to the PC. That disaster in Ammon Jerro's Haven? It happens when she is forcibly separated from the PC by a teleport.