12 down
Wonderful
piece
of
writing
showing
power?
(11)
Wonderful piece of writing showing power? (11)
hints
0
checks
0
hints
The definition is at the end of the clue.
How the clue works
Look at showing power? — that's your definition, since a superscript number is exactly how you'd denote a mathematical power or exponent. Then the wordplay builds it up as a charade: SUPER meaning wonderful, followed by SCRIPT meaning piece of writing.