p.boxed
  | Move twice at every turn.

p.
  The only difference with orthodox chess is the double-move rule,
  but this affects the game a lot.

p.
  At the very first move of the game, white make only one move - as usual.
  However, after that and for all the game each side must play twice at
  every turn. The goal is to checkmate.

figure.diagram-container
  .diagram.diag12
    | fen:rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR:
  .diagram.diag22
    | fen:r1bqkbnr/pppp1ppp/2n5/4p3/2B1P3/5Q2/PPPP1PPP/RNB1K1NR:
  figcaption.
    Left: after the moves 1.e4 e5, the 'd' pawn is pinned.
    Right: the black king is under check.

p.
  In the diagram position on the left, after the first black move ...e5,
  the 'd' pawn is pinned because moving it would allow 2.Bb5,Bxe8 capturing
  the king.
  On the right, after 2.Qf3,Bc4 black king is under check because of
  the options 3.Bxf7,Bxe8 or 3.Qxf7,Qxe8.

h3 En-passant capture

p.
  Capturing en-passant is allowed under certain conditions.
  If the opponent moved a pawn allowing such a capture (once or twice),
  then (to take it) you must capture en-passant at the first move of your turn.
  After that, if (and only if) there is another en-passant capture available
  you can play it on the second move.

p.
  Note: if a pawn 2-squares jump was made and then a piece landed at the
  en-passant square at the second move, a pawn capture on this square
  takes only the piece.
  And, if a pawn advanced twice then en-passant capture
  on its first movement is impossible (the pawn is now "too far").

h3 More information

p
  | This variant is derived from 
  a(href="/variants/Doublemove1") Marseillais chess
  | . It is also playable 
  a(href="https://greenchess.net/rules.php?v=double-move") on greenchess
  | .