What move would you do here? (Blacks Move)

B x g7

Then 0-0-0

Only move.

HOWEVERif I looked long enough I would play Bxg7.

You are the 2nd one to tell me that, thanks

No, the best move is Bxg7

No matter what black does he is lost

resighn

You can't

The Queens in the way

Black h8-g8

If white take f8 and promotes, black takes with king.

This leaves  White's exposed queen to capture, making White move; then black can save bishop at g4?

I'm done

@EnergeticHay (National Master)

"I see. The position just looks bad for black though - the g7 pawn is kind of unstoppable and if you take it, the threat of Qxg7 attacking the h8 rook is too much to handle as black is already down a piece in the initial position"

Bf8Xg7-then white should move Qg5XBg7
Then we can move in the Rh8-Rf8 then white will take the h8XBg4. That bishop will die either way.
After this, we can Castle the King to the queenside. and secure both Rooks but the Kings side will be destroyed later for the black side but because White hasn't opened its queenside pieces well we can gain an advantage after this Castling.