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All answers having "I'm impressed!" as clue:

3 Character Answers:

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GEE

OOH

WOW



4 Character Answers:

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DAMN

NICE

OOOO



5 Character Answers:

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BRAVO

NEATO

OHWOW



6 Character Answers:

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NOTBAD

OHNICE



8 Character Answers:

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VERYGOOD