68 challenges across eight tiers. Tier 8 is a warm-up; tier 1 will take an evening. Nothing is locked — play them in any order.
The boss. Is the black king attacked by anything at all — pawn, knight, bishop, rook, queen or the white king?
Eighty-one cells. Match the grid only when no digit repeats in any row, any column, or any 3×3 box.