Puzzletober 2025: Blunder

Rules: Determine who won each game of the tournament. The rules and events of each of the three rounds are provided in the narrative below. No games end in a tie or forfeit. 

Ande leans against one of the green walls of the event room and thanks everyone for coming. Everyone else at the hotel is seated at a table in front of a chessboard. The boards are unset, and all the pawns are missing, but this is intentional.

Ande asks the pairs to decide who goes first, then reveals the rules. "For the first round, players take turns placing a piece into the center 4x4 region of the board. Both players should have the full back rank of a traditional setup, meaning it should be possible to fill the region if both players place every piece. White goes first; white's first turn is free, but every subsequent placement must attack the last piece that the opponent placed. The game ends when a player is unable to place a piece. Whoever places the last piece loses."

Some people misunderstand the final rule and try to lose in this round instead of win.

The first game to end is the match between the economist and the diver, which only lasts six turns. They both place only one of their knights each, with the diver placing the knight sometime after the economist.

The next game to end is between the bowman and the innkeeper, which also lasts six turns. The bowman places both his knights.

The game between the clerk and Ophelia lasts nine turns, with the eighth turn forcing the ninth to be a losing move. It starts with all four bishops being placed in a diamond shape. The next four turns are knight placements. During the game, the clerk places a piece in the center of the bishop diamond.

In the game between the farmer and the newcomer, the farmer places exactly seven more points of material than the newcomer, with the king being worth 3.5 points. Every piece type is placed at least as many times as it appears in the starting set of pieces, but only one piece type is placed by both players.

After the winners meet for the second round, Ande reveals the new rules. "This round is the opposite of the previous. Players still take turns placing all the back-rank pieces into the center 4-by-4, but black goes first; black's first turn is free, but every subsequent placement must be attacked by the last piece that the opponent placed. The game ends when a player is unable to place a piece. Whoever places the last piece wins."

The first game to finish in this round ends in a win for black after white blunders on their first turn. Black's first turn was not a blunder. The player in this game who placed more bishops in the first round places no bishops in this round.

The second game to finish in this round is between the winners of the six-turn games. Neither player makes a one-move blunder in this game. The player in this game who placed more knights in the first round places no knights in this round. Black's first turn allows two options for white. Black's second turn is a queen placement. White's second turn forces black's third turn to be a certain piece in a certain place. White's third turn attacks one of black's previously placed pieces.

After the winners of the second round shake hands, Ande begins to reveal the rules for the third round. "Scanning for attacks in the previous rounds was really just practice for this round. To begin, I'd like both of you to choose two pieces from your back-rank set." The player whose game finished first in the second round chooses the piece they won with in the second round for one of the two pieces, and the other player does not select this piece at all. Ande gathers two more chessboards and asks the players to each sit in front of one with the bank of four pieces that were selected. Ande also does so on the third chessboard. He says, "Now, the goal is to construct the smallest ouroboros you can out of these four pieces. Every piece in the ouroboros must attack a piece and be attacked by a piece in a way that forms a loop of captures. Pieces are allowed to attack ally pieces. I'll assist with arbitration in this round and also set an example. Let's see." He thinks for a bit and eventually concludes, "Well, it just so happens that the pieces you chose make it impossible. I'm going to give a queen to all of us to make it possible." He sets up an example on his board. "All you have to do is make the smallest ouroboros the fastest. Size will be judged by how many tiles wide the setup is in both directions. For example, I have pieces on the first and eighth ranks, and on the A and G files but not the H file, so the size is eight times seven. You are only allowed to claim one solution, but if it's a tie, whoever claimed it first wins. I hope that made sense." The players nod and study their pieces.

(This round is inspired by Chess Loop.)

The player whose games in the first two rounds took combined fewer turns claims the number 9 followed by the number 16, whereas the other claims the number 6 followed by the number 12. These first claims were valid if and only if they were possible to achieve, and each second claim was either looking for another solution for fun or a backup from getting the first incorrect.