Brushing up on my combat and adversaries for this weekend's game.. still new with BC-- is there a key to the statblocks that explains what each entry means? I couldn't find anything like this in the Adversaries chapter, or is it in one of the other core rules books?

I could probably sort of fake it, but it seems like this must be buried somewhere (??)

Not 100% sure what you mean but take a look at page 34 (Characteristics) in the core book.

Sorry if not clear.. I mean in the Adversaries chapter, the actual statblocks for the monsters/adversaries themselves. There are abbreviations such as "TB" and there are small red numbers above the larger black numbers in the Toughness column... is there a key to what these notations mean/are?

that would be the unnatural stats and TB is toughness bonus