Also known as Crazyhouse (drop chess, mad chess, reinforcement chess, turnabout chess and schizo-chess), the Loop Chess was always my all-time favorite of all chess variants I implemented at BrainKing.com (I think the final count was 37).
Although this variant of chess adheres to the same rules and initial setup as the standard game, it stands out as one of the most fascinating and enjoyable versions due to a significant difference. What you capture becomes your extra weapon to drop on the board as a sudden strike. Creepy, huh?
Let me demonstrate it on a simple game:
1. e4 ♞f6 2. ♗c4 ♞xe4 3. ♘f3 ♞f6? (This is a typical mistake in this variant. Black ignores the threat to sacrifice the bishop at f7, which is much more lethal because of the extra piece placement.)
4. ♗xf7+! (White gets an extra pawn.)
4. … ♚xf7 5. ♘g5+ ♚g8 (And Black is doomed.)
A longer full game is always the best way to explain the details. Watch and enjoy: