p.boxed
  | Pieces can fusion and also be split under certain circumstances.

p Fusion Chess is played like FIDE Chess with the following exceptions:

h3 Fusion

p.
  A non-royal simple piece (Knight, Bishop, or Rook) may combine with
  another simple piece on the same side (including a King) by moving
  onto its square.

p The combined piece moves as either of the two pieces just combined:
ul
  li King + Bishop = Pontiff
  li King + Rook = Dragon King
  li King + Knight = Cavalier King
  li Bishop + Rook = Queen
  li Bishop + Knight = Paladin
  li Rook + Knight = Marshall

p A piece may not combine with
ul
  li another piece of the same type,
  li a piece belonging to the opponent,
  li a compound piece.

p.
  A King may not move to combine any piece, though other another
  piece may move to combine with its King.

figure.diagram-container
  .diagram.diag12
    | fen:r1bqkbnr/pp1ppppp/2n5/2p5/4P3/5N2/PPPPBPPP/RNBQK2R:
  .diagram.diag22
    | fen:r1bqkbm1/pp1ppppp/2n5/2p5/4P3/5D2/PPPP1PPP/RNBQK2R:
  figcaption Before and after moves BxNf3 and RxNg8.

h3 Fission

p.
  An unattacked compound piece may split by moving one
  of its components, under its own powers of movement, to an empty square.
ul
  li A Rook which separates from a piece must move away as a Rook moves.
  li A Bishop which separates from a piece must move away as a Bishop moves.
  li A Knight which separates from a piece must move away as a Knight moves.
  li A King which separates from a piece must move away as a King moves.
p The compound piece is replaced by the component which doesn't move away.

h3 Other details

p Any piece that has participated in fission or fusion may no longer castle.

p Pawns may promote to Rook, Bishop, or Knight only.

p.
  The object is to checkmate your opponent's current royal piece, which may
  be a King, Pontiff, Dragon King, or Cavalier King.

p.
  No royal piece may move through check when moving more than one space.
  For the Cavalier King, the Knight move is understood as beginning
  orthogonally and turning diagonally or vice versa. If both spaces
  it might pass over to reach a square are checked, it cannot move there.
  However, this does not limit its ability to check or attack a piece.

figure.diagram-container
  .diagram
    | fen:r3br2/c2p4/1pd2pqp/p1B5/1D1P1QP1/8/PPP1P2P/2RG2N1 c8:

p.
  On the diagram above, the Cavalier King only non-splitting move as a Knight
  is to c8. Indeed, a6 and b6 are under attack. b8 as well, but not b7.

h3 More information

p
  | See the 
  a(href="https://www.chessvariants.com/other.dir/fusion.html")
    | chessvariants page
  | .

p Inventor: Fergus Duniho (1999)