I recall seeing a number of chess games where a lot of pieces are involved in the final checkmate, and was curious to know what is the maximum number of pieces of one player A that have been involved in a checkmate of the other player B, where a piece is said to be involved if and only if removing it either causes B's king to be no longer in check or causes one of the squares around B's king to be no longer attacked by A's pieces. It is easy to construct a reachable position where 9 pieces are involved, and to prove that no more than 9 pieces are involved. It is also possible for all 6 types of pieces to be involved. For example:
[White "Checkmate"] [Black "9 pieces involved"] [FEN "6B1/7K/2N5/5kP1/2R1P2P/8/6N1/3Q4 w - - 0 1"]
But are there any actual competitive games that ended with such a checkmate (i.e. using 9 pieces)? If not, what is the maximum number ever used in a competitive game? Among these games, what is the maximum number of types of pieces used? I exclude non-competitive games merely to avoid contrived games.
Note: As John Coleman pointed out in the comments, this notion of "involved" is more like "critically involved" because it is possible that a checking piece is covering another piece that would also provide check if the first was removed, or that a piece next to the checkmated king is protected by more than one piece. One could consider a variant notion of "loosely involved" defined as follows: A piece X of A is loosely involved in a checkmate of B if and only if we can remove some pieces of A that attack B's king or a square next to B's king such that it is still a checkmate and X is (critically) involved. I think this should cover such cases, so I am fine with including examples that use this looser definition of "involved".