2 | Move twice at every turn.
5 The only difference with orthodox chess is the double-move rule,
6 but this affects the game a lot.
9 At the very first move of the game, white make only one move - as usual.
10 However, after that and for all the game each side must play twice at
11 every turn. There are two exceptions:
15 If the first move gives check (maybe checkmate),
16 then a second move isn't played.
18 If no move is available after the first move, then it's stalemate
19 and again, there is no second move.
22 About the PGN game notation: when a side plays two moves in a row,
23 they are separated (in order) by a comma in the PGN.
24 Example: 3.Na5,Bd3 e6,f4 (the two first are white moves,
25 the two others are black moves).
27 figure.diagram-container
29 | fen:r1bqkbnr/pppp1p1p/2n5/4p2p/4P3/5N2/PPPP1PPP/RNB1KB1R:
30 figcaption After the moves 1.e4 e5,Nc6 2.Qh5,Nf3 g6,gxh5
35 Capturing en-passant is allowed under certain conditions.
36 If the opponent moved a pawn allowing such a capture (once or twice),
37 then (to take it) you must capture en-passant at the first move of your turn.
38 After that, if (and only if) there is another en-passant capture available
39 you can play it on the second move.
42 Note: if a pawn 2-squares jump was made and then a piece landed at the
43 en-passant square at the second move, a pawn capture on this square
45 And, if a pawn advanced twice then en-passant capture
46 on its first movement is impossible (the pawn is now "too far").
52 a(href="https://www.chessvariants.com/multimove.dir/marseill.html")
54 | page on chessvariants.com.
57 | Inventor: Albert Fortis (1922) - disputed according to
58 a(href="https://fr.wikipedia.org/wiki/%C3%89checs_marseillais#Histoire")
59 | this historical note