My favorite chess variant is Horde, because unlike all of the other variants (with the exception of 960) it doesn't force you to play chess differently. For example, Three-check forces you to play extremely defensively while king of the hill often forces you to play extremely undefensively. But Horde is a whole different game.
The pieces still move the same, but the goal for white is to capture all of the black pawns. This is most easily acheived by getting to the back of the horde. The weakest files are the a, and h file, as those pawns are only defended once. The easiest way to immediately create pressure on either of those files is 1. a4 (or h4). This forces the b5 (or g5) pawn to choose between capturing or being captured, and thus opening up the file for the rooks.
White will often have to make sacrifices (bishop or knight for 2 pawns). These are best when they can significantly weaken a file or diagonal to access the backrank.
The goal for black is to checkmate. This is most easily achieved after promotion (by which time white will probably resign after all of their sacrifices). As aforementioned, black's weakest files are the a, and h files. Black must guard these files and the backrank. Black must remember that the power is in the horde, and therefore must not spreadout his pawns in an easily permeable, checker like structure. Accept or reject sacrifices as the position calls for. Black must also keep in mind that should white get to the back of the horde, it's not always the end of the game. It takes valuable time for white to capture all of the pawns rank by rank -- time black could be using to promote pawns. And if all else fails, it's often quite possible for black to play for a draw -- stalemate -- when black has no legal moves.
The pieces still move the same, but the goal for white is to capture all of the black pawns. This is most easily acheived by getting to the back of the horde. The weakest files are the a, and h file, as those pawns are only defended once. The easiest way to immediately create pressure on either of those files is 1. a4 (or h4). This forces the b5 (or g5) pawn to choose between capturing or being captured, and thus opening up the file for the rooks.
White will often have to make sacrifices (bishop or knight for 2 pawns). These are best when they can significantly weaken a file or diagonal to access the backrank.
The goal for black is to checkmate. This is most easily achieved after promotion (by which time white will probably resign after all of their sacrifices). As aforementioned, black's weakest files are the a, and h files. Black must guard these files and the backrank. Black must remember that the power is in the horde, and therefore must not spreadout his pawns in an easily permeable, checker like structure. Accept or reject sacrifices as the position calls for. Black must also keep in mind that should white get to the back of the horde, it's not always the end of the game. It takes valuable time for white to capture all of the pawns rank by rank -- time black could be using to promote pawns. And if all else fails, it's often quite possible for black to play for a draw -- stalemate -- when black has no legal moves.