Chess is one of the oldest games on the planet, so it only makes sense that someone, somewhere, would begin to create variations of it to spice things up. Crazyhouse chess is just one of those variations and is very popular, especially for Internet players. Crazyhouse chess has its own specific rules, although the game itself is based on regular chess. All the pieces move the same as in the classic game, and no pieces explode or become something else. Pawn promotion and castling are the same, but there are some aspects of this variant that sets Crazyhouse chess apart.
Capturing pieces and pawns operates the same in Crazyhouse chess as it does in the classic game, with one exception. Each enemy piece you take becomes yours to use against your opponent, and vise versa. For instance, if you trade your bishop for an enemy knight, on your next turn you can place the knight that used to belong to your opponent on any vacant square on the chess board. Likewise, your old bishop now belongs to your opponent, and can be placed on any vacant square whenever they wish, as long as it is their turn.
The same rule applies to placing pawns on the board, with one exception. On your turn, if you have enemy pawns you are holding, they can be placed on any square except first and eighth rank ones. That is, you can place a pawn at b7 where it will have the ability to promote on the next move, but you cannot drop it on the b8 square and call it a queen.
Placing with Check
In some variants, you cannot place a piece on the board if it gives check at the same time. Crazyhouse chess allows it, and in fact, some spectacular checkmates are possible because of this rule. The notation for a move like that would be, for example, N@f7+. This tells us someone has placed a Knight on the f7 square, and that it gave check at the same time. Knights tend to be very valuable in the Crazyhouse chess variation.
Opening and Playing Tips
When opening in a Crazyhouse chess game, it is best not to leave holes in your position, because pieces and pawns love to occupy holes. As a general rule, do not fianchetto the bishops (place them on b7, b2, g7, or g2) as you might in normal chess openings. This creates a huge target and your game can crumble quickly.
Also, be careful when castling, because it is easy to castle directly into a mating attack, especially when it is hard to predict what pawns or pieces may just crash into your position.
When attacking, do not stop if at all possible. Keep throwing checks and limiting the enemy king, because the second the attack lets up you can be sure that your opponent is going to counter, and things can get brutal very quickly when you have no more pieces to place for defense.