Chess and I: click here for the homepage.
November 2024.
§1 Some possible variations on the rules of Spartan Mirror
On the Alt Site of PyChess (pychess-alternates), one of the available variants is Spartan Mirror (Alt Site link here). Spartan Mirror derives from Steven Streetman's Spartan Chess (PyChess link here), but can be seen as an elegant and fascinating independent chess variant, which could intrigue a lot of chess fans. It's very chess-like, but none of the pieces is the same as in standard chess, kings being the only exception -- and a partial exception, since each player has two half-royal kings.
Streetman's Spartan Chess is an asymmetric variant. For that reason, it has very delicate balance issues. Instead, Spartan Mirror is as symmetric as standard chess, so that proposing fairly good variations on the rules is certainly much easier.
It think it would be interesting to test the following proposals, especially 1, 2 and 3:
1. Reverse symmetry: opposite starting positions for the major pieces on files b and g (so as to discourage early crowned rook exchange on the b-file).
2. Variations on kings:
2a. No duple check or duple checkmate (that is, a player who still has both kings is never in check).
2b. Even more than two same-colour kings allowed, via promotions (in that case, each king will be 1/3-royal, 1/4-royal etc., instead of half-royal; the duple rule can be adapted likewise, if one decides to keep it).
3. One could allow en passant capturing (Berolina-style, of course):
3a. En passant is allowed only if the relevant square on rank 3 or 6 is not already occupied by a piece or hoplite. [Default choice.]
3b. If the relevant square on rank 3 or 6 is already occupied by an enemy chessman, the capturing hoplite takes the enemy hoplite and the other enemy chessman too, in the same move. [Too complicated or strange? Yes, probably.]
4. Major pieces:
4a. Knight-rook hybrid instead of rook-king hybrid.
4b. Knight-king or bishop-king hybrid instead of knight-bishop hybrid.
4c. Some other choice for the major pieces (including Q, NQ, NRK, NBK, special/divergent hybrids, etc.).
5. & 6. To leap or not to leap [I'm not enthusiastic about the leaping variations: just a bit curious]:
5a. No leapers at all.
5b. The hoplites are not leapers (for the two-square advance).
5c. The captains and the lieutenants are not leapers (for their two-square moves).
5d. The knight-bishop hybrid is not a leaper: it becomes a xiangqihorse-bishop (aka Paradigm dragon).
6a. All pieces are leapers, and/or some kind of hoppers, for all of their movements (excluding one-square moves, of course).
6b. The knight-bishop hybrid is a leaper, or some kind of a hopper, on the diagonals too.
6c. The rook-king hybrid is a leaper, or some kind of a hopper.
7. & 8. Castling allowed (same general conditions as in chess or in 960, but the check-related rules have to be stated in detail):
7a. The simplest castling idea: (queenside) the c-file king and the b-file major piece swap their position; (kingside) the f-file king and the g-file major piece swap their position.
7b. A weird alternative: (c to g) c-file king moves to g-file and g-file piece to f-file; (f to b) f-file king to b-file and b-file piece to c-file.
7c. Both 7a and 7b are legal castlings.
8a. Each player may castle only once.
8b. Each player may castle twice, that is with both kings.
8c. Opposite castlings only (that is, each player may castle only once, and you can't castle with your c-file king if your opponent has already castled with his/her c-file king; the same is valid for the f-file kings).
9. & 10. Minor pieces:
9a. One-square moves only (that is, the captains become wazirs and the lieutenants become similar to ferzes).
9b. One-, two-, and three-square moves allowed.
10a. The peaceful (one-square) movement of the lieutenants is vertical instead of horizontal.
10b. Both vertical and horizontal peaceful movements are allowed.
10c. The captains are allowed peaceful (one-square) diagonal movements.
11. Fischerandomization (one should decide on the exact constraints, also depending on the ruleset choices).
12. Combinations of Spartan Mirror and standard chess: for example, standard chess with Spartan captains (or lieutenants) in the place of the rooks; or standard chess with Spartan minor pieces in the place of knights and bishops; or Spartan Mirror with rooks (or knights or bishops) in the place of the captains; or Spartan Mirror with a queen (or a rook) and only one royal king per player, in the place of the two half-royal kings... There are a lot of possible combinations.
Some further notes:
Knight-rook hybrid instead of rook-king hybrid (4a): that was the initial idea for Streetman's Spartan Chess, later modified due to the balance issues. See this YT video, 8:08 (Dev Interview! How Spartan Chess was designed and balanced).
I suppose some of my proposals could be tentatively tested for Spartan Chess as well. In particular, points 2 (no duple check, and/or more than two kings), 3 (en passant), and some form of 7-8 (castling).
§2 On standard-chess-based variants with more than one royal king per player
In April 2024, I read about New Army / Different Armies chess variants for the first time. Some of them looked beautiful and interesting, especially Spartan Chess and Synochess, and it was clear that PyChess was the most important website for anybody who likes such games. (There was no Spartan Mirror yet.)
The most exciting feature I learned about was the half-royalness of the two Spartan Chess kings per player, including the special rule of duple check and checkmate. I thought it would be amazing to adapt that feature (two half-royal kings per player) to standard chess.
The simplest idea is replacing the queen with the second king, and keeping everything else as in standard chess. (See my page On player-friendly piece design, section §3, about half-royalness symbols/diacritics.) Well, some additional rules should be stated as regards castling, and promotion too. We might choose strictly Spartan-like rules. In that case, we should have the following simple variant:
No castling (but take a look at my proposals 7-8 in section §1 above, and at the rules of Dual, Weak Dual, and Royalty Transfer Chess on greenchess.net).
We keep the Spartan Chess duple rule (but see my proposal 2a in section §1 above, and the greenchess.net rules).
Pawns can promote to the pieces that are present in the initial setup: so, no queen is allowed if there is no queen. -- Promoting a pawn to a king is legal, if and only if you have only one king left (but see my proposal 2b in section §1 above, and the greenchess.net rules again).
One engaging subvariation in the initial setup: you can replace the a-file rooks with (potentially castling-involved) queens.
I still think this would be a very good and sober chess variant. I can see it as one of the most intriguing fulfilments of my proposal 12 in section §1 above (Combinations of Spartan Mirror and standard chess).
In April 2024, being enthusiastic about the discovery of half-royal kings, I took a long series of notes on the possible subvariants of "4K Chess / Four Kay Chess / Four-King Chess", as I thought it could be named. It was the first time I tried to invent a chess variant, and I didn't absolutely know that, several weeks later, I would have other ideas and would write a web page on My own heterodox chess, where Spartan Chess is barely mentioned.
At present, I don't know if the details of my "4K Chess" subvariants are interesting. Probably not. In April, I wrote my notes about possible left-right symmetric subvariants vs. left-right asymmetric subvariants (it's about internal symmetry in each player's starting position); subvariants with the two standard rooks per player and no queen (see above), or with two potentially castling-involved queens per player and no rook; subvariants with one regular rook and one potentially castling-involved queen per player (see above, "One engaging subvariation in the initial setup"); other subvariants with only one rook per player, and the second king in the starting position of the other standard rook; subvariants with only one knight per player, and the second king in the starting position of the other standard knight. In addition to that, I considered some (sub)variations on the castling rules (only one vs. two castlings per player, etc., similarly to proposal 8 in section §1 above), and some piece swapping in the starting position, or even overall fischerandomization.
One of the reasons why my enthusiasm for the idea of "4K Chess" started to drop, last Spring, was that I found out that the idea was not new. There were already a lot of standard-chess-based variants with two kings per player; and at least one of them actually had Spartan-style half-royal kings (but without the duple rule).
In most variants with more than one royal piece per player (usually royal kings), each royal piece is fully royal: if even only one of your royal pieces is attacked, you are in check/checkmate, as if the other royal piece(s) didn't exist. In my opinion, the Spartan-style feature is more subtle and intriguing.
Among the variants with more than one royal piece per player:
Coregal or Co-regal, by V. R. Parton (1897-1974). Both the king and the queen (!) are fully royal. It can be played on pychess-alternates and, with different castling rules, on greenchess.net.
Two Kings, to be played on the Fairy-Stockfish playground (but you have to download a comprehensive version of variants.ini).
Three Kings, also to be played on the Fairy-Stockfish playground. No actual royal piece, but you lose the game when one of your kings is captured.
The last mentioned website, greenchess.net by Uray M. János, describes and includes Weak Dual Chess too, which has half-royal kings (as I call them), that's what we were looking for. Royalty Transfer Chess, on the same website, is another similar variant, with different rules.
Still another kind of shared royalness is to be found in the variant Rex Multiplex (link here), on www.janko.at.
A number of relevant variants, including some of the above, are listed and described in the large and substantial book The Classified Encyclopedia of Chess Variants by D. B. Pritchard (second edition, completed and edited by John Beasley, 2007) -- download it from here, jsbeasley.co.uk/encyc/encyc.pdf. In particular, see pages 81 ff., 10.2 Changed or multiple kings (within Part 1, Games using an ordinary board and men); and pages 175 ff., 19 Changed or multiple kings, especially 179 ff., 19.6 Multiple kings present from the outset (within Part 2, Other games using square lattice boards). But, as far as what I call half-royalness is concerned, we can only reference to Double-King Chess by D. Moeser (1970), and Prince Chess by J. W. Brown (1997), on pages 181-182. We can add some of the variants of section 19.2 Substitute kings: at least Heir Apparent Chess by S. Lewis (1995), on page 177, which is rather similar to Prince Chess. All the three mentioned variants are large-board variants, and none has the duple rule -- which is probably a Spartan Chess original innovation.
Another important source is George Jelliss's website, mayhematics.com. On the page A Guide to Variant Chess: Chess Problem Terms (link here), 2002, under the heading Multirex, we read: "The possibility of having more than one royal piece on each side has been experimented with from time to time and is known as multirex or rex multiplex", etc., with further explanations and distinctions, but no reference to playable variants -- the page is about chess problems.
To conclude this section, I'd like to bring greater attention to the already mentioned variant Weak Dual Chess (greenchess.net), which can be said to realize the idea I independently came up with some months ago, with two half-royal kings per player.
In Weak Dual Chess, as in the related variants Dual Chess and Royalty Transfer Chess (all three designed by Uray M. János himself, personal communication), each player has two kings, one queen, and only one bishop. That's one of the many possible combinations -- and I thought this one should be disfavoured, because of the emphasis we usually put on the bishop pair in chess. Anyway, I have now tried Weak Dual Chess. I like it. As already touched upon, it's without the duple rule; and it allows more than two same-colour kings via promotions. (That's not crucial of course, since having three or four kings is not so useful -- queens and rooks are better. But we like formal details, don't we?)
Personally I can hardly bear correspondence games. Nonetheless, I recommend the interesting and enjoyable Hungarian-based website greenchess.net / zoldsakk.hu. Some of the variants it includes are really rare and precious.
§3 Multiple kings on nine-column boards (9x9 or, better, 9x8)
(Sections §3 and §4 are appendices to the previous one, On standard-chess-based variants with more than one royal king per player. I wrote them one month later -- end of December 2024.)
I can say I'm against chess variants on large boards. The usual 64 squares are enough, and even standard chess is a very complex game, of course. If we want to modify or increase the intricacy of the game, we have a lot of possibilities, and I think that adding new files or new ranks is not among the most elegant and interesting ones.
Anyway, when I was writing section §2 above, I had some interest in J. W. Brown's 9x9 variant called Prince Chess. On page 182 of The Classified Encyclopedia of Chess Variants by D. B. Pritchard (second edition) we read:
Prince Chess (John W. Brown, 1997). Board 9x9; each side has 1 x Q, 2 x Prince, R, B, N, 9xP; baseline RNBPrQPrBNR. Prince moves like K with an initial option of a three-square leap forward (including diagonally forward) if not under attack. One B can move one vacant square orthogonally initially provided both Bs on the board. Pawn-two allowed, promotion only to a piece previously captured. If one Prince is captured, the other reverts to a king when the object is checkmate. (Meta-Chess)
It's similar to greenchess.net Weak Dual Chess and to my personal idea on variants with half-royal kings, but has a larger board, no castling, and some other arbitrary rules in the place of castling. (By the way, "promotion only to a piece previously captured"? Why? And is one allowed to promote to a prince?) J. W. Brown's princes are, in my terms, half-royal kings without the duple check rule; as such, either of them becomes a regular (fully royal) king if the other has been captured. As for "One B can move one vacant square orthogonally initially provided both Bs on the board", I later found out that several heterodox variants with an uneven number of files (usually nine files) have such a rule, that is one or another version of the bishop adjustment/conversion rule (see below).
J. W. Brown's Prince Chess is interesting, but I wouldn't say I'm looking forward to playing this variant as it is proposed. These are my reasons:
9x9 is a large board. I would be more comfortable with 9x8, that is with only eight additional squares.
Castling or not? Castling or... leaping forward? Castling is the only strange and illogical part of the standard chess ruleset (grandmaster Vladimir Kramnik's opinion). Brown's Prince Chess is a no-castling variant and, ok, that's not a flaw. But why introducing new arbitrary rules such as "an initial option of a three-square leap forward"?
I think that bishop adjustment/conversion rules are also bizarre and unnecessary rules. Not very elegant, not entirely chess-like. Choosing an initial setup other than RNB...BNR would be better, in order to have different-colour-squared bishops from the beginning. (This problem has already been encountered and solved in different ways, for several 9x8 and 9x9 variants -- see below.)
Let's quote the entry on Heir Apparent Chess too (The Classified Encyclopedia of Chess Variants, page 177). One of the differences, in comparison to Prince Chess, is the size of the board, 9x8 instead of 9x9:
Heir Apparent Chess (Stephen Lewis, 1995). Board 9x8; extra piece is an Heir Apparent; baseline (a1-i1/i8-a8) RNBQKHNBR. H moves as Q but up to three squares; if the K is mated, H assumes the role of K and now moves as a K. Checkmate or capture K and H to win. (Variant Chess 19)
I have tried to collect a good amount of information about standard-chess-based variants on 9x8 and 9x9 boards -- with my personal preference for 9x8; but, as a matter of fact, several 9x8 variants are improved or modified versions of pre-existing 9x9 variants. (Keywords for web search: 9x8, 9×8, 9 by 8; 8x9, 8×9, 8 by 9... You can also go to the query form in the bottom part of the page www.chessvariants.org/index/mainquery.php and fill in the cells "Board Rows:" and "Board Columns:".)
(There also exist standard-chess-based variants with one or more additional ranks, that is proper 8x9, 8x10 etc. boards. We are not dealing with them, but here are some links, including four playable subvariants of greenchess.net Far Chess ["The two armies start farther from each other than in chess"]: Far chess – 9, Far chess – 10, Far chess – 11, Far chess – 12, Farther Chess in M. Hayes's website; we can add at least the following: D. Howe's Chess on a Longer Board with a few Pieces Added, A. Alvarez de la Campa's Templar Chess, J. Aikin's Eight-Stone Chess.)
The already discussed J. W. Brown's Prince Chess is played on a 9x9 board. As for 9x8 boards, The Classified Encyclopedia of Chess Variants by D. B. Pritchard gives only a handful of variants (in general: not only multiple-royal ones). Beside the already quoted Heir Apparent Chess, there are D. Trouillon's Ultra Chess and G. Kuzmichov's Active Chess on page 114, Bird’s Chess by H. E. Bird on page 121, L. P. D'Autremont's Angel Chess on page 122, M. Horne's Chancellor Chess on page 124, R. Keene's Flexichess and Varichess on page 185, and Duell aka Conquest on page 294. Here's a quotation about Ultra Chess and Active Chess (page 114, within section 13.3 Rectangular boards -- with some innocent typos):
Ultra Chess (reported and perhaps originated by D. Trouillon, early 1970s). Board 9x8 (a1 black); baseline (a1-i1/a8-i8) RNBQKQBNR. The array places both white bishops on black squares, both BBs on white squares. Trouillon’s favoured solution was was that a player, once in a game, could transpose adjacent B and N (‘mini-castling’) provided neither had been moved; an alternative, preferred by John Gollon, was to change the baseline to RBNQKQBNR. (Correspondence between John Gollon and Philip Cohen)
Active Chess (G. Kuzmichov, 1989). Board 9x8; baseline (a1-i1/a8-i8) RNBQKBNRQ. This is effectively the orthochess array with an extra queen and pawn on the i-file; an alternative places the extra Q at g1/g8. The idea for the game came to the inventor on reading The Ninth File by A. Karpov and A. Roshal. Kuzmichov was the editor of the Riga magazine Sahs and an official youth trainer. His pupils rigorously play-tested the game to establish the optimum array. (Manuscript note presumably derived from personal communication)
Active Chess (indeed a questionable name!), in its main subvariant RNBQKBNRQ, can be played on greenchess.net, link here, beside a very similar variant, Superqueen Chess II, where one of each player's two queens is replaced by a knight-queen hybrid, link here. The latter has been invented by Uray M. János himself, "by combining Active Chess with superqueen".
Let's add some further web links on other more or less similar variants, either 9x8 or 9x9, from diverse sources (some already seen in Pritchard's book): Chancellor Chess and M. Horne's Modern Chancellor Chess; G. Vicente Maura's Modern Chess and Prime Ministers Chess; Dukes Chess; Eagle Chess; J. Carrillo's Hia Chess; Valery Bannykh's Chesston; Chessplus; L. P. D'Autremont's Angel Chess, link 1 and link 2.
The already mentioned problem of different-colour-squared bishops is solved in different ways by the different variants. Some solutions are more, or less, brilliant than others. For example, the RNB...NBR setups may be seen as awkward, because the pawn (or square) in front of one bishop is unguarded -- or, at least, it's not controlled by the standard pieces. Conversely, the last mentioned variant, Angel Chess, has crowned bishops instead of regular bishops: there is no colour-bound piece, as in Paradigm Chess30. That's an original solution, that may look very modern (Angel Chess was designed in the 1910's!).
As already touched upon, a widespread alternative is keeping the RNB...BNR setup and adopting the Bishop Adjustment Rule (link here) or the Bishops Conversion Rule (link here), or other similar ad hoc conventions.
Now, all that considered, this question arises: If we want to adapt greenchess.net Weak Dual Chess to a 9x8 board, putting back all the bishops, what are the most advisable choices? (Remind that the greenchess.net multiple-king variants have only one bishop per player.) We won't go through the huge number of possible initial setups. Actually I'll consider only the most obvious or widespread setups, according to my review of other standard-chess-based variants on 9x8 and 9x9 boards (see above), plus a few others.
1 Initial setups.
1.1 Left-right symmetric setups:
1.1.1 The most obvious solution is standard-chess-like RNBKQKBNR, and I suppose it's a good one.
1.1.2 Already-castled setups (kingside-like castling on both sides): BKRNQNRKB; NKRBQBRKN.
1.2 Other standard-chess-like setups, adding the second king or the queen on the a-file (or the i-file):
1.2.1 Regular QK in the centre: KRNBQKBNR.
1.2.2 Also standard-chess-like, but KK instead of QK in the centre: QRNBKKBNR.
1.3 Setups with regular different-colour-squared bishops from the beginning:
1.3.1 Castling-friendly setups: RNQBKKBNR; RNQKKBBNR.
1.3.2 Already-castled setups (kingside-like castling on both sides): BKRNQBRKN; NKRBQNRKB.
1.3.3 Already-castled setups on one side only, with the other king in or near the centre: NKRBQKBNR; NKRBKQBNR; etc.
2 Castling rules.
2.1 No castling at all. It's a possible choice, with any initial setup. (When you have two half-royal pieces, castling is much less needed than in standard chess -- see Spartan Chess, where the Spartan army has no castling option.)
2.2 Castling allowed. Same general conditions as in chess or in 960.
2.2.1 Castling and check. The check-related rules for castling have to be stated in detail. The rules of the greenchess.net multiple-king variants can be taken as the default: Weak Dual Chess in particular, if our variant has half-royal kings.
2.2.2 Castling movements. On a large board, with two kings and two rooks, and a variety of different initial setups, several choices are possible. As a standard-chess-oriented player, I prefer this kind of castling: the castling-involved king moves two squares -- always two squares -- in the direction of the castling-involved rook, the rook jumps over the king and lands on the square next to it. (If this is our choice, on a 9-column board a king will never castle a-side if its starting square is on files a or b, and will never castle i-side if its starting square is on files h or i. See also Castling: which king with which rook? below.)
2.2.3 Castling: which king with which rook? Several choices are possible, again.
2.2.3.1 In the greenchess.net multiple-king variants, on a standard 8x8 board and with both kings in the centre, all four combinations are allowed. On a 9x8 board this can be our choice too, especially for the initial setups where both kings have their starting squares on the three central files (see 1 Initial setups above).
2.2.3.2 Alternatively, each king may castle only with the rook on the same side (as a consequence, kings starting from files a, b, h or i cannot castle at all).
2.2.4 Castling: how many times?
2.2.4.1 Each player may castle only once.
2.2.4.2 Each player may castle twice, that is with both kings.
2.2.4.3 Opposite castlings only.
3 Mirror symmetry or reverse symmetry (for all starting positions other than 1.1 Left-right symmetric setups).
3.1 As a standard-chess-oriented (and 960-oriented) player, I prefer mirror symmetry: the black queen faces the white queen, etc.
3.2 However, you may well choose reverse symmetry, aka rotational symmetry: chessvariants.org links here and here.
4 Solving the issue of different-colour-squared bishops (for all starting positions other than 1.3 Setups with regular different-colour-squared bishops from the beginning -- strictly standard-chess-oriented players will obviously prefer the 1.3 setups).
Some of the solutions (bishop adjustment/conversion rules; crowned bishops in the place of normal bishops) have already been reported on this page. Here I propose a much more comprehensive list of possibile solutions, most of them with fairy pieces in the place of bishops -- they are the same of Niekerk and Willenberg's variant Paradigm Chess30, plus my Modified versions of Paradigm Chess30 (section §2 of the web page My own heterodox chess):
replacing the bishops with bishop-xiangqihorse hybrids (as in Paradigm Chess30);
bishop-xiangqihorse hybrids with peaceful horsing (meaning that the horse move cannot be a capture);
bishop-knight hybrids;
bishop-knight hybrids with peaceful knighting;
non-royal bishop-king hybrids (aka crowned bishops);
peaceful-crowned bishops;
weakened peaceful-crowned bishops: horizontal-only (peaceful one-square movement sideways, like Spartan Chess lieutenants);
weakened peaceful-crowned bishops: vertical-only;
keeping the standard bishops but adopting or customizing one or another version of the bishop adjustment/conversion rule.
5 Royalness rules, and promotion to king.
I prefer multiple-king variants with half-royal kings, such as Weak Dual Chess (without the duple check rule), and Spartan Chess and Spartan Mirror (with the duple check rule). However, my 9x8 adaptations of multiple-king chess should work with any royalness ruleset.
5.1.1 Half-royal kings, no duple check rule.
5.1.2 Half-royal kings, duple check rule.
5.1.3 Fully royal kings.
5.1.4 No royalness, that is no check or checkmate: the objective is to capture both (or all) enemy kings.
5.1.5 Choose or invent other royalness rules.
5.2.1 Promotion to king allowed, if and only if you have only one king left.
5.2.2 Promotion to king always allowed.
5.2.3 No promotion to king.
(Dark and light squares with reference to 9x8 and 9x9 coordinates: as a standard-chess-oriented player, I say square a1 should always be dark -- it's only a formal convention, of course.)
In conclusion, let's try to make it short: Which would be my favourite subvariant of 9x8 Weak Dual Chess, so that I'd like to play hundreds of games on greenchess.net or other platforms, if it were implemented?
We'll certainly choose one of the Setups with regular different-colour-squared bishops from the beginning, most probably RNQBKKBNR, which is so sober and castling-friendly.
Castling as in Weak Dual Chess, but each king may castle only on its side: one king castles a-side, the other castles i-side. (The castling king moves always two squares. As in Weak Dual Chess, each player may castle twice, that is with both kings.)
Mirror symmetry, of course.
Royalness rules as in Weak Dual Chess, including promotion to the half-royal piece. The only subvariation I'd really like to keep, as the players' free choice, is the duple check rule variable: a. no duple rule, b. duple rule.
If I could select a few other subvariants of 9x8 Weak Dual Chess, my choice would be Left-right symmetric setups with not too powerful hybrid bishops:
a. basic RNBKQKBNR (castling rules as above), b. and c. two already-castled setups BKRNQNRKB, NKRBQBRKN (no further castling!).
Let's replace the regular bishops with fairy pieces: a. horizontal-only peaceful-crowned bishops, or b. bishop-xiangqihorse hybrids (aka Paradigm dragons), or c. bishop-xiangqihorse hybrids with peaceful horsing.
All the rest as above, including the duple check rule variable: a. no duple rule, b. duple rule -- the players' choice.
(Two half-royal kings, perhaps with the duple check rule, and peaceful one-square movement sideways for the diagonal minor pieces: how many Spartan Chess distinctive features!)
§4 Combining Knightmate with Weak Dual Chess: Weak Dual Knightmate
Let's go back to standard 8x8 boards. So comfortable.
Well, while writing the previous section, I had an idea: standard chess initial setup, multiple-royal variants, Knightmate and royal knights... all put together. It's a nice and ready chess variant!
Two half-royal knights and a non-royal king per player.
Short-like castling allowed on both sides (only the rook moves, since the knights are already on the b- and g-files); each player may castle twice.
Royalness rules as in greenchess.net Weak Dual Chess, including promotion to the half-royal piece. (You can promote to non-royal kings too, but queens and rooks are much stronger. Non-royal knights are not allowed.)
Only two subvariations -- the players' choice:
[For Spartan Chess fans:] duple check rule;
[For long castling lovers:] if you castle queenside, the resulting position is the same as in standard chess, so that the knight has to move as well: (half-)royal piece on the c-file, rook on the d-file.
If Weak Dual Knightmate were made available on greenchess.net or anywhere else, I'd really love to try it.
(As for sets of pieces and graphics, I maintain that one should never use a normal king piece or symbol for non-royal kings. See section §3 of my page On player-friendly piece design. But the non-royal king symbols used for Knightmate and other variants on pychess-alternates and on greenchess.net are already good and unambiguous.)
§5 Spartan Chess and Spartan Mirror over the board
How to play Spartan over the board? Do I need to be a wood carver?? In my opinion, you don't. See the photographs in sections §1.4, §1.5 and §1.6 of my chess pictures page.
As you will see, I considered Spartan Mirror crazyhouse too. We just have to decide on what conditions you are allowed to drop a king and to promote to a king (see 2b in section §1 above). Based on the same principles, one can also play Spartan Mirror bughouse -- with no need for cardboard tiles or the like, except for promoted hoplites.
(I think that crazyhouse and bughouse adaptations of proper Spartan Chess would be straightforward as well: through capturing and dropping, multiple kings are allowed for every player, including the standard chess armies. The standard pawns promote to standard pieces, and the hoplites promote to Spartan pieces; when captured, the promoted pieces turn back into pawns/hoplites. -- There exists a Bughouse Spartan Chess designed by the game's inventor himself, Steven Streetman, link here, with different rules: "there are 3 Orthodox and 1 Spartan side between the 2 boards"; "A Spartan King when captured and passed becomes a hoplite". Not a regular and symmetric form of bughouse.)
Half-royal?
H. G. Muller's term extinction royalty is probably more adequate than mine. See his very interesting analyses on Spartan Chess, links here and here.