In a certain chess game, White mated in his sixth move by playing gxf8=N. Reconstruct the game!

For people not used to this notation: if we label columns from a (at the left) to h (at the right), there was a white pawn in the 7th row of the g column, that took a black piece in the 8th row on the f column, was promoted to a Knight, and mated the black King.