Nearlytriple Raumschach

As with Grossraumschach, my 4-player Raumschach enlarged only enough for each army's Unicorns to cover the board between them (note how doubling just the Unicorns and their Pawns filled out the 6x6x6 board's equivalent of a Raumscach camp) I turn the board through a right angle so that the camps run vertically. This is partly to avoid the imbalance of one player advancing from the top down and t'other from the bottom up and partly to allow a 4-player subvariant with each player sitting at their own vertical edge of the board.

Setup

Level a

Level b

Level c

Level d

Level e

Level f

Level g

The 4-player subvariant can be extrapolated by arranging additional armies along the empty edges of the board.

Pieces

As simple pieces are weak in 3d (although the Knight is an exception on the original Raumschach board), promotee pieces are compound. Following my convention of calling 26-directional pieces Emp-eror/-ress, I allow promotion to Empress but also to Queen (R+B only), Duchess (R+U), Marshal (R+N), Governor (B+U), Cardinal (B+N), and Cavalcade (U+N). All promotees are unbound.

Rules

There is no initial double-step move, En Passant, or Castling.

Pawns reaching a cell on the board's opposite-colour edge must be promoted to either an Empress or a compound of two simple array pieces.

In the 2-player subvariant Check, Checkmate, and Stalemate are as in FIDE Chess. In the 4-player one a Checkmated player, that is, one threatened by the player about to play, loses their Emperor but their capturable pieces remain in place but immovable. These may be captured and reintroduced Shogi-style as pieces of the capturing player, but without demotion back to Pawn. As with Grossraumschach, finalist armies may well differ greatly in size, but the stronger might still need all that strength to Checkmate the weaker!

Notes

The possibility of a 4-player subvariant is specifically possible due to the low piece density that Nearlytriple Raumschach inherits from Raumschach itself.

7x7x7 is an interesting size of board as 7x7 is the smallest back rank on which a royally-restricted piece can Castle or Cathedral with a choice of eight different pieces in a face-to-face 3d variant. In the notes on Hourglass Hex Chess I have considered such ranks in the context of a hex-prism variant, which has the advantages of unbinding the Bishop, but on a cubic board Cathedralling with the ordinary Bishop would not really do. One idea that I had was to use Stewardess, Waitress, Valet, and their Contra- pieces - an idea that developed into using their short-range versions and pieces divergent between the 2:n:1 leapers. This inspired the Churl, Samaritan, and Obeyer of Man and Beast 19, which in turn gave me the idea of a variant called Churlish Chess, another example of English self-deprecation like my 2d variant Knavish Chess. I envisage the back rank:

Xs Qr Sd Ws Sd Qr Xs
Xn Qs Bt Ca Bt Qs Xn
Oy Cl Bn Es Ad Cl Oy
Ss Cw Qn Er Ds On Ss
Sn Cy Pc Gv Dk Cy Sn
Cc Cv Wr Su Wr Cv Cc
Vt Xd Cb Ws Cb Xd Vt