p.boxed
  | Every captured piece can be re-used by the capturer,
  | landing it anywhere instead of moving a piece.

p
  | Orthodox rules apply, with only one change:
  | every time a piece is captured, the capturer "reserve" of pieces is
  | augmented with this figure. At every move, you may choose to land one of your
  | reserve pieces anywhere on the board (except first and last ranks for pawns),
  | instead of playing a regular move.

p.
  Move notation: an arobase '@' indicate piece landing. For example B@d4 means
  a bishop rebirth on d4 square, and @f3 is a pawn landing on f3.

figure.diagram-container
  .diagram
    | fen:qnbrkb1r/ppNppp1p/2p2p2/8/8/5N2/P1PPPPPP/1RNQKBNR:
  figcaption After 1.b3 Nf6 2.Bxf6 gxf6 3.Nf3 c6?? 4.N@c7#

p.
  Note: capturing a promoted pawn put a pawn in the reserve,
  not the promoted piece. This is to allow to gain material on last rank without
  fear of giving a queen to the opponent.

h3 More information

p
  | This variant is very popular, a possible starting point is 
  a(href="https://lichess.org/variant/crazyhouse") lichess.org
  | .