The most common and most likely answer to this crossword clue is the 6 letter word MIMICS
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More clues leading to the result MIMICS
Buddy explains!

The straight part
We know that "impressionists" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impressionists = mimics.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 MIMICS mean?
MIMICS noun- A person who practices mimicry, or mime.
- An imitation.
- To imitate, especially in order to ridicule.
- To take on the appearance of another, for protection or camouflage.