Legal position?

Saw this one in another thread. Is it legal?

Black's light squared bishop was captured by a white knight (as was Black's entire queenside), and a black pawn was promoted to a light-squared bishop.

Legal, yes, but improbable in practical play.

 Actually, it's not quite that simple.

Chess960?

 This isn't from an actual game. The question was whether the position is LEGAL or not (in regular chess, not 960). As far as that question goes, you oversimplified the position in your first post.  

Thanks for clarifying the question. Now, please correct your criticism. I took a stab; you claim I have "oversimplified". I might be missing something, but it is not from oversimplification. Even more important, I did not simplify the position even if my answer failed to account for the cause of the anomalies. Find a more appropriate word for the nature of my error.

My initial answer was based on a few assumptions: the board is oriented correctly; it is normal chess. You specified neither of these.

As neither player is in check, the principal problem of legal moves leading to this position appears the absence of Black's queenside piece that could not have moved--the bishop--and its existence on the board.

My notion that a knight munched the missing pieces is not entirely necessary if the Black king has moved; a rook or queen could have done the damage, just as Black's queen and rook could have moved out after the bishop was captured.

That Black has a light-squared bishop, and has b- and d-pawns on their starting squares proves that an underpromotion occurred.

Yes, it is a legal position, but it is an unlikely one.

I'm having trouble figuring out how to get White's c-pawn to capture over to g8 to promote to a light-squared Bishop, since the original one on f1 can't have found its way to d5. I see that White can capture one Black pawn, a Queen, and one of the Rooks, but the other Black pawn had to have promoted to the Black light-squared Bishop. This leaves White with three captures to move four files over. What am I missing?

Now that I think of it, I'm not even sure how Black's promoted Bishop escaped from the square on which it promoted, unless it found enough captures to get over to the Queenside (which I think it can).

 You're not missing anything, and are absolutely right. This position is illegal because there is no way to account for White's light-square bishop on d5. Black's f-pawn could,indeed, have reached the queenside to promote, but the key is that this leaves only three captures for White's c-pawn to make (and as you said, it would need four captures to reach a light square on the eighth rank).

 Sorry, I was trying not to give anything away (If I just said "You're wrong, it's NOT legal," then the answer would be right there for everyone to see.), and ended up using poor wording. I meant to say there was more to the problem than what you had mentioned (the second misplaced bishop), so that anyone who looked at this would not assume you had it without even looking at the diagram. 

You might have said, "you're missing something in your analysis." That would have told me that I was wrong without giving away the legality/illegality at issue.

I cannot believe I was so blind as to miss the White pawns/bishop.

Thanks for the puzzle.