Villager Chess

Players open a villager's trade screen and press the Play Chess button to start a game against that villager. The villager's trading level sets how strong the opponent plays, so a Novice is a pushover while a Master is close to unbeatable. A fresh Novice gives a free win, and a player who wants a real fight is advised to trade the villager up to Master first. The mod uses a from-scratch pure-Java chess engine with a 0x88 board, full move legality and Zobrist hashing, and its move generation is verified against perft reference counts. The search runs on a background thread, so the game does not stutter.

The server owns the game state and clients only send move attempts, which leaves little room for cheating with a modified client. Rules are enforced in full, and draws are recognized when a position repeats, when the move count reaches the limit or when neither side has enough material to mate. Walking more than 16 blocks away from the villager, the villager dying or disconnecting ends the game as abandoned. A player can resign with a button that closes the board. Stakes and rewards are optional, and the mod fits villager trading setups on servers. Installation needs Fabric API.