Drill the checkmates every player must own. Random starting positions, real engine defence, scored on how cleanly you finish.
Each card is a foundational mate. Start with King and Queen versus King. Every player learns this first.
The board sets up fresh every time. You learn the technique, not memorised moves.
The lone king plays the longest defence Stockfish can find. No cheap shots.
Three stars for near optimal play, two for solid, one for any mate within the move limit.