Normal sudoku rules apply. Cages show their sums, and digits cannot repeat within a cage. On thermometers, digits increase from the bulb. But! One of the digits from 1-9 is a ghost, and is not bound by those constraints. The ghost digit still follows normal sudoku rules (appearing once in each row/column/box), but does not count toward cage sums, can repeat within a cage, and can appear anywhere on a thermometer (other digits on the thermometer must still increase from bulb to tip; the ghost digit is simply ignored).