Overview
Forest breaks the habit of the square board. Levels run on 6x7, 8x6, and other stretched or squeezed rectangles, and that alone reshapes the game: reach is lopsided, the center is not where your eye expects, and a bishop's diagonal leaves the board early in one direction. Pawns show up more here than in most other worlds, and their short reach fits the tight geometry.
The Mechanic: Non-square boards
Forest bends the board itself. Levels play on rectangles that are not squares: 6x7, 8x6, 7x8, and other cuts. It sounds like a small change until you place a rook and its row runs longer than its column. Every piece's reach turns asymmetric, diagonals exit the board sooner on one side, and the patterns you trusted on a square grid need a second read.
Pieces in this world
Rook
Bishop
Knight
PawnRooks, bishops, knights, and pawns, which are rare in other worlds
Level progression
Starts on gentle 6x7 and 7x6 boards with one or two pieces. Later levels stretch the rectangle further while piece counts climb to four.