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All answers having "Make a mistake" as clue:

3 Character Answers:

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ERR



4 Character Answers:

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GOOF

SLIP

TRIP



5 Character Answers:

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FLUFF



6 Character Answers:

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GOOFUP

MESSUP

SLIPUP



7 Character Answers:

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BLUNDER



12 Character Answers:

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DROPACLANGER



13 Character Answers:

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FUMBLETHEBALL