The basic idea is this:
You start out with your king, queen and three pawns. You can place them wherever you want; however, be careful, the enemy appears anywhere at the top row of the field.
In this image, the player decided to place the three pawns around the queen in the lower right of the field. Every turn you can cast a die and place any of the following based on your roll:
1: Pawn
2: Rook
3: Knight
4: Bishop
5: Second Queen (Can be killed)
6: Second King (Can be killed)
If no pieces are available, the default piece is Pawn, if no more pieces are left to use (you can use white and black figures), you win the game. That means the game has a maximum of 32 rounds.
Also in the image above, you see that the enemy has thrown one die, and got a four. A "monster" is summoned, a stack of four coins, each coin representing one life point.
Every turn the enemy moves each "monster" towards the king and/or queen by one field in any direction. If it is within attacking distance of the player's figures, the attacks are calculated and subtracted from a monster's total points. No coins remain - the monster is gone.
The player's figures attack as they would normally do in a regular chess game, but return to their position immediately afterwards. Example:
The pawn attacks a monster with six coins, reducing it by one.
The knight attacks a monster with four coins, reducing it by one.
This goes on, until there are no queens and kings on the field, in which case, naturally, you lose.
Additional rules could include:
* You can't close your maze, of course. There has to be a path towards your kings and queens. You can hide a king behind a queen, since it would eventually open up the path if attacked and killed.
* If the enemy rolls 6, they can either spawn a monster with six coins, or regenerate a monster in the field by 1 (not more than six).
* If the enemy rolls 1, they can either spawn a monster with one coin, or split up one coin from an existing monster (creating two monsters, but at a remote location). The new monster must be placed directly next to the monster it was detached from (the direction is probably irrelevant).
* If the player is too overpowered (and I think that might be the case), you could add an additional rule: Once a figure has attacked a monster, put the figure on the ground. It will only stand up again in the next round, meaning it will skip one round of the enemy and not attack.
* Queens, rooks and bishops have ranged attack and always return to their original position.
* Kings and Queens instantly kill any monster, regardless of how many coins they have, but always die themselves. You should not use Kings and Queens for your maze walls.
* The enemy could (and probably should) be played by an actual second player.
* And lastly, if a tower kills a monster, put a coin underneath it. For every coin received this way, it deals an additional +1 damage.