Unfortunately, a piece density of 0.5 seems the limit, not to mention the fact that a third line of pieces cramps the board (the Knights in Chess on a Longer Board cannot move immediately without some extra rule) and prevents a quick attack on the King. (Admittedly, there could be a first line of Pawns, a second line of Orthochess pieces and a third line lurking behind the Orthochess pieces.) This brings us to some hard choices.
Rooks or Bishops are clearly legitimate, but when it comes to divergent pieces, there are more possibilities, and only the Orthochess Pawn and the Xiangqi Cannons have yet stood the test of time on Earth, although I'm persuaded that on some faraway planet, some kind of Murray Lion cavorts with the Knight around the Rook and the Bishop. It becomes even less obvious with baroque types. It seems just as legitimate to borrow one or two of them, but the choice of that (those) type(s) is not straightforward. Indeed, when you play Withdrawer Chess or Coordinator Chess, you already long for the other Ultima types, just as you crave for Queens and Bishops when you play Xiangqi or for Cannons and their oblique equivalents when you play Orthochess.
I guess David Howe doesn't have that problem, because he wanted only one divergent piece and one baroque piece. The Pawn was already divergent. As for the baroque piece, the Withdrawer is the most interesting Ultima piece, and the other candidates were too strong - or too contrived, like the Coordinator. So, it was the right choice in context but I would prefer to use weaker baroque types and get more leeway.
Some types need much downsizing before they can fit with Orthochess.
V.R. Parton's Chimaera, which is an uncapturable Swapping Queen type, is downright unplayable. The Immobilizer is also too powerful, and the lack of Chameleons in Immobilizer Chess implies that the side which loses his Immobilizers alone usually loses the game. (The Witches in my Jacks and Witches 84, though less mobile, present the same characteristic.)
Stratomic features the Nucleas, which teleport on any square
and explode with all their non-royal neighbors. The idea of the Nuclea
is great, but I don't believe the Nuclea should explode early. It is
the possibility of the explosion which makes it valuable.
(In Invasion, which doesn't use Orthochess types, Jean-Louis Cazaux has Flags which turn on a Bomb when they reach one of two special squares. This is much more satisfactory, but, here again, often that condition becomes a win in itself. I prefer a condition which ensures that if one player strikes, his opponent will get a return shot.)
None of the aforementioned games features rifle capture, which is an enticing idea which seldom turns into an enticing game. Rifle Chess loses much from the inability for pieces of the same type to attack each other (except by discovery check), and a Rifle Queen would be far too potent. I also wanted baroque types myself when I invented Bilateral Chess. Since I was unwilling to waive immobilization, displacement or baroque capture, I came up with two piece types at the expense of four Pawns. The Pawn deficit was already a flaw, but another flaw was the use of a Wizard which had eight non-capturing moves and eight rifle capture moves. (It had also five rifle immobilization moves.)
Indeed, I should have begun with whatever pieces I found fully legitimate, and dropped the others at a later time, when the position had opened up.
It is played on a 12 x 8 board.
The King, Queen, Rooks, Bishops, Knights and Pawns move as they do in International Chess, except when they are orthogonally adjacent to a Wizard.
The Lion and the Can(n)on are not new.
Before its first flip, the Can(n)on is set to move Rook-wise.
The other pieces may be dropped only after both Kings have moved, and before any King has reached the eighth row.
In the present game, there are four types of Halflings, which all move like a Halfling Queen (there is a slight difference for the Leaper) and have baroque capture.
Once both Kings have moved, a player may drop as a move a pair
of Halflings on a pair of empty symmetric squares on its first
rank. He may drop the Leapers on b1 and g1, or b8 and g8, the Pincers
on a1 and h1, or a8 and h8, the Advancers on z1 and i1, or z8 and i8,
the Withdrawers on y1 and j1, or y8 and j8. His opponent will have to
drop the same pair of Halflings on the corresponding squares, which
often means he will have to free those squares. It may take him some
time or disorganize his forces.
Meanwhile, he will play with an inferior army.
To the Wizard, the Kingside and the Queenside are bent against each other. The Wizard moves as a Ferz, one square diagonally, or as a mirror Wazir , that is, it first reaches the symmetrical square on the same rank, which need not be empty, and then moves as a Wazir. Thus it is usually colorbound.
The Wizard may swap with enemy pieces, to the exception of Elephants
and Golems. It also alters their mobility. An enemy piece which is
orthogonally adjacent to a Wizard is only permitted a non-capturing
Wazir's move, one square orthogonally. Thus a Bishop or a Wizard which
is getting away of a Wizard has to change color square.
(That neutral Wazir move affects neither the Elephants nor the Golems, which are immune to wizardry, nor the Pawns nor the Assassins, which cannot move or capture when they are orthogonally adjacent to a Wizard.)
A Pawn which captures a Wizard suffers a serious change of metabolism. It becomes a Golem. A Golem is a two-square diagonal piece appearing on the late Wizard's square and on the Pawn's starting square. The two parts of the Golem, which must remain connected, move each as a mirror Firz, that is, first to the symmetric square on the same rank, which need not be empty, and then one square diagonally. (Thus the Golem's path is color-changing.) The Golem captures by replacement. Like the Wall, the Golem may capture two pieces at once, but is captured when either of its parts is captured, by replacement or otherwise.
Like the Wizard, the Elephant is a not-too-straight right-to-lifer. It
rotates around its King, clockwise or contra-clockwise, on an
eight-square pattern which is intended to generalize the pattern of
the Windmill in Alexandre Muniz's The Royal Standard. That
pattern contains the squares which are distant of an eighth of the
square orbit revolving around the King.
(If an Elephant in c3 is adjacent to its King in c4, the pattern is c3, d3, d4, d5, c5, b5, b4, b3, c3 - clockwise -, or c3, b3, b4, b5, c5, d5, d4, d3, c3 - contra-clockwise. If the Elephant is in b2, a Knight's move from the King in c4, there are sixteen squares which are at a two-square distance from the King: b2, a2, a3, a4, a5, a6, b6, c6, d6, e6, e5, e4, e3, e2, d2, c2, b2, and the pattern is b2, a3, a5, b6, d6, e5, e3, d2, b2 - or the other way round : all the squares which are a Knight's leap distant to the King, The remaining squares, which are an Alfil or a Dabbabah's leap distant to the King, constitute the other Elephant pattern of, say, size 2. Similarly, there are three eight-square patterns of size 3. One reunites the squares which are three squares orthogonally or diagonally away from the King, the two others mix squares which are a Camel's leap distant to the King with squares which are a Zebra's leap distant to the King. There are four patterns of size 4, and so on. Of course, those bigger patterns are incomplete, and the Elephant cannot cross the limits of the board to reappear on the other side. Only the King's move will change the orbits of its Elephants.)
The Elephant doesn't capture, so if the two immediate squares, clockwise and contra-clockwise, are not free, it simply cannot move. But only an enemy King, Pawn or Thunder may take it. An enemy Wizard cannot alter its move or swap with it. An enemy Can(n)on may not hop over it.
Besides, a player who captures an Assassin now owns it, and is free to drop it later, like in Shogi or Chessgi, as long as no King has reached the eighth row.
A Pawn which has been swapped to its starting line is permitted a two-square advance. A Pawn which has been swapped to its first line is permitted a two or three square advance (or a one-square advance followed by a two-square advance). Extended en passant applies.
A Pawn reaching the eighth row promotes to any non-royal officer, including all four Halfling types, to the exception of a Golem. However, there are restrictions for Assassins and Thunders.
A Pawn may promote to an Assassin only if there is one empty square where it can put the King in check, in which case the move is completed by the teleportation of the new Assassin to such a square. (If the Pawn move has created a discovery check, the new Assassin must still put the King in check by contact, or by covering a Can(n)on.) A Pawn may promote to a Thunder only if both Kings see each other once the Pawn is on the eighth row, in which case the move is also completed by the explosion of the new Thunder anywhere on the board. Anyway, since the Pawn is already on the board, it is not a drop situation, and it doesn't matter whether both Kings have moved or either has reached the eighth row.
If a Pawn reaches its promotion zone by swapping, the owner of the Wizard decides how to promote it, but isn't allowed to promote it to an Assassin or a Thunder.
If a Pawn advances to the eighth row and becomes orthogonally adjacent to a Wizard, it promotes before getting bewitched - unless it promotes to an Elephant, of course -, but may not promote to an Assassin or a Thunder.
If a Pawn captures a Wizard on the eighth row, it becomes a Golem and is unable to promote.
An Assassin may shoot en passant a Pawn on the eighth row which has become an Assassin, and retrieve that Assassin if neither King has reached the eighth row.
An Assassin may shoot en passant a Pawn on the eighth row which has become a Thunder and has already explosed.
A Wizard on a central file may commute as a mirror Wazir to its current position.
An Elephant whose eight-square pattern is empty may rotate to its current position.
A swapped Wizard may swap back its swapper.
A bewitched Can(n)on may not flip, either without moving, or while completing its neutral Wazir move.
An Assassin may not shoot en passant a Can(n)on on a square when the
Can(n)on is hopping over that square and wouldn't be allowed to land
on it. However, an Assassin may always shoot en passant a Halfling as
if it were a Halfling Queen.
(Yes, even when the Halfling is a Leaper and the only square of the Leaper's path within the Assassin's capture zone was occupied and jumped over by the Leaper.)
The early middle game features the drop of a pair of Halflings whose entry squares force an already belated opponent to reorganize his position. (The other player may try to keep his King unmoved, but such a strategy is not without risks.) The Halflings - often the Leapers, whose entry squares on the b and g files have been long abandoned by the Knights - and the Assassins usually help the player who has already the upper hand. (An Assassin on the seventh rank prevents the Rooks from centralizing, and gives sometimes a shot to one Leaper on its entry square.)
The late middle game has some Xiangqi flavor. There are Can(n)ons, the Lions are rather lame, and one of the Kings may have to escape the vision of its opposite number. It also features only two or three riders, leapers or Halflings for each side against a pair of Elephants and a pair of Wizards, which are both defensive. The Elephants aren't easy to maneuver. As for the Wizards, they may be quite effective as a pair when it comes to catch or repel a Queen, a Rook or a Can(n)on, but a single Wizard - or a pair of same-color Wizards - is useful only against an Assassin or a Pawn. Golems are less protected than the Walls in Chess on a Longer Board.
Pawn promotion doesn't happen before the hundredth move, but it still happens more often than not, although the Halflings, the Wizards and the Elephants are quite skilled at slaughtering, swapping or blockading the Pawns.
I pitted two pairs of baroque riders, Halfling Advancers, Leapers or Rifle Queens with so-called Fools - in fact Slip Queens, which march an odd number of squares in any direction. Those Fools - Withdrawers, Coordinators or Pincers - didn't behave so badly, but the late middle game featured only one or two capture-by-replacement pieces other than the Kings and the Pawns.
I experimented with a pair of Drago(o)ns, Polypieces which were either Fergus Duniho's Dragon in British Chess or the Nightrider, but they kept forking King and Queen.
I forged five pairs of Wizards, only one of which would have been dropped. Those Wizards, which would have moved first to the symmetric square on the same rank, and then as a Queen, were Immobilizers - leading to easy captures of Zillions pieces -, Swappers - leading to indiscriminate Pawn promotions -, uncapturable and uncapturing Diplomats - leading to a lot of 200-move games -, Creators spawning a Pawn on their departure squares when those departure squares were on a file deprived of Pawns - leading to Pawn chases reminiscent of Chaplin's Modern Times, and Protectors letting friendly pieces advance forward through themselves like the Wall - which barely happened once a game.
I also gave each player two Assassins. They had a tendency to end the game before the other pieces were dropped.
Finally, I wanted to make the Golems more resilient, but then the owner of the Wizard couldn't allow their formation.
Diversity is the key characteristic, and perhaps later versions will steal from the strangest future variants, although the armies are probably big enough. Anyway, like in Chess on a Longer Board, there is a flip piece, a Halfling and baroque capture, but the Golem doesn't live long enough to be more than a cosmetic two-square piece.
There is a zrf file.
(Since Zillions doesn't take into consideration capture modes, I added bogus points. You can open the zrf and change the relative values of pieces with commands such as (1000-points) or (5000-points).)