The most common and most likely answer to this crossword clue is the 8 letter word TRICKERY
I've seen this crossword clue in Independent
T
R
I
C
K
E
R
Y
Buddy explains!

The straight part
We know that "What Puck uses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what puck uses = trickery.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRICKERY mean?
TRICKERY noun- Deception or underhanded behavior.
- The art of dressing up; imposture.
- Artifice; the use of one or more stratagems.
- An instance of deception, underhanded behavior, dressing up, imposture, artifice, etc.