Historical note (skip if you like):
In this interesting puzzle @TSLF asks for the "maximum number of black and white pieces that are involved in a checkmate position".
Originally, they left much open to interpretation, and interpret me and a handful of others did!
My interpretation did not exactly win, but I actually quite like it, so I decided to make a separate question of it.
Construct a legal position where white to move mates in one, subject to:
- The mate is unique. Update: This riddle smith is not above the law as layed down by the World Federation for Chess Composition in their Handbook of Chess Composition, article 13(2) with footnote 16 (thanks @trolley813) where it says: "[...] except that in the final move a promotion into different pieces having partially the same power (for example queen/rook or queen/bishop) may be tolerated.
- Removing any piece except a king results in a legal position (white to move, i.e. white king may be in check, black king mustn't).
An "accessory to regicide" is any piece which when removed leaves a position where white can no longer mate in one.
Your task: Maximise the number of accessories.
A "witness" is a non-king piece that is not an accessory. For those not well versed in the fine art of regicide: A perfect regicide is one where there are no witnesses. Let us define the regicide score as number of accessories - 3 x number of witnesses
Bonus task: Maximise the regicide score.
Perfectly valid example per article 13(2) and footnote 16 of the Handbook of Chess Comoposition:Faulty example (thanks @Magma who points out that the Nc8 cannot be removed without creating an illegal position.)