Originally dropped, Mo Kudus performs! It requires thinking outside the box (6)
I believe the answer is:
sudoku
'box' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for sudoku that I've seen before include "Number game" , "Numerical puzzle" , "numbers in boxes" , "Numeric puzzle" , "(Usually) nine-by-nine numbers puzzle" .)