Babylonian Chess

This chess variant can be played with a standard chess set and 
polyhedral dice (aka RPG dice). Having additional chess pieces 
make for a more aesthetically pleasing game. Added variation by 
playing with a hexagonal or 3-player chessboard may also be 
possible.

Rules

All normal chess rules apply with several exceptions. All pieces 
move  in the normal manner and special movements like en passant, 
castling and promotion are allowed. The main difference is that a 
player does not automatically capture an opponent's piece. When a 
player advances a piece with the intention to capture an 
opponent's piece, both players must roll dice appropriate to their 
pieces. The piece with the lower roll gets captured. Tied rolls 
results in stalemates.

The dice assignments for the pieces are as follows:

Pawn:	1d4
Knight:	1d6
Bishop:	1d6
Rook:	1d8
Queen:	1d12
King:	1d20

If the advancing piece is captured, the defending piece remains 
in place. An exception to this is the King (see below). In 
addition, several other differences exists:

1) Players need only declare a checkmate, not a check.

2) Pieces can be moved to expose the King to attack unless 
such a move will result in an immediate checkmate.
   
3) A player who already has a piece that can capture the 
opponent's King may, during any of his subsequent turns, 
move another piece into a position that threatens the King 
and claim an "Assist" attack. In this way, a player's King
may be simultaneously attacked by several pieces which are in 
positions to do so. In this case, the dice rolls of the 
assisting piece and all the attacking pieces are combined 
and compared against that of the King. If the King rolls
higher, all the attacking pieces are captured and the King 
has the option to move into any one of their positions, even 
if it is more than one square away. If the attackers combined 
roll is higher, the King is captured and the game
ends. In the event of a stalemate, the King can choose to 
convert the attacking piece with the lowest roll to his color.
   
4) A checkmate immediately wins the game, no dice rolls need 
be made.

5) The game ends when a player captures or checkmates his 
opponent's King.

Notes

The introduction of the dice roll element forces players to 
weigh between the risks and benefits of trying to capture 
enemy pieces. This also means that the best made plan could 
be undone by an unlucky roll of the dice. The King, having
a d20 dice roll and having special rules, can be used creatively. 
On the whole, the game becomes more unpredictable and exciting 
with considerable possibilities for new strategies and 
counter-strategies.