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Indeed, it is quite amazing that two pieces with so few moves can force the bare King into a corner. They seem to cooperate very well when standing next to each other, as a self-protecting pseudo-piece covering 2 squares, leaving the King free to close off other escapes. But 8x8 is the largest square board where they manage that. The reverse piece, mFcW is even better at this, and can still force checkmate on 10x10. (But being effectively color bound, only for the pair on unlike shade.) It cannot self-protect, but is good at preventing the bare King to approach them, when standing next together. Ferzes would probably be even better at this, but cannot execute the final checkmate even when the bare King is cornered.

There indeed is a special version of the 2-vs-1 Applet that configures the piece move from the URL. The problem for having something similar for 3-vs-1 is not technical, but the use case. Two identical minor pieces are almost never capable of forcing the checkmate. So you would want to present the piece of interest with a partner that would allow it to force the mate. OTOH, you don't want the mate to be mainly the achievement of that other piece. (Like it would be when you pair it with a Bishop, which can force checkmate together with virtually any piece on any size board.)