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All answers having "Harmful" as clue:

3 Character Answers:

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BAD

ILL

SEE



4 Character Answers:

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EVIL



5 Character Answers:

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MAXIM



6 Character Answers:

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NOCENT



7 Character Answers:

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MALEFIC

NOCUOUS

NOISOME

NOXIOUS

WESTERN



8 Character Answers:

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DAMAGING



10 Character Answers:

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PERNICIOUS



11 Character Answers:

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DELETERIOUS

DETRIMENTAL

SCAREMONGER