Goodman Games

Do Thieves get their Backstab bonuses (including the extra powerful damage die and automatic crit) when flanking an opponent or just when the opponent is completely unaware of the Thief?

Judge's call. I've been ruling that Warriors can use a Mighty Deed to set up thieves for the backstab...

That's a nice "move" caveman, I'm going to tell my Warriors to steal that.

If it was logically plausible, such as in the woods, or in a dark room or full of rubble (and bodies) AND my the thief asked, I'd make them do a "sneak" check (which ever made the most sense) if they succeeded (DC = 3d6+HD), she can get her back-stab bonus & auto-crit. She was awesome, but she's dead now.

I like that idea. I think I'll just keep the Backstab as "situational" and let the players work out ways in which they can create the situation.

the wording in the book is set up as there being two separate circumstances (defined by the use of the word "or"), those being "behind an opponent," and the other "or otherwise unaware."

I plan on using it just like that, so a thief gets backstab whenever the target doesn't know of the attack before hand, or when the thief is actually behind the target - with a "if the monster isn't focused on fighting you, you can probably manage to get behind him unless he has an ally or wall at his back," rule in place of actual facing rules.