Captured:
Tap (or drag) your White King (♔) and other pieces to move them by standard chess rules — get your King to the top row to clear the floor, and Black replies automatically after every move. As you play, you're building your own chess board out of the pieces you capture: every capture goes into your Captured pool, a pawn reaching the second-from-top row promotes by spending a captured piece of that type, and surviving pieces each bring one captured pawn back with them as an extra White pawn on the next floor. Only pieces standing on the top row when your King arrives carry over — and a piece moved onto the top row is committed: it can't move again, but Black can never touch it there.