The most common and most likely answer to this crossword clue is the 6 letter word ELFISH
I've seen this crossword clue in Independent
E
L
F
I
S
H
More clues leading to the result ELFISH
- It’s mischievous and egotistic to go topless
- Life’s changed alongside husband, distraught
- Mischievous use of the Hispanic angle
- Fantasy language may support second word for greedy
- Mischievous angle anticipated by European left
- Mischievous leaders in seventh heaven after the Spanish provided backing
- The Spanish place for audience that’s mischievous
- Playful after school or greedy?
Buddy explains!

The straight part
We know that "Mischievous" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mischievous = elfish.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 ELFISH mean?
ELFISH adjective- Characteristic of an elf; elfin, elven.
- Mischievous.