Was beastly deceptive! (5)

I believe the answer is:

foxed

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'deceptive' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives can occasionally define each other.

I cannot understand how the rest of the clue works.

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(Other definitions for foxed that I've seen before include "a bit off-colour" , "Deceived in vulpine manner" , "Baffled" .)

I've seen this clue in the Evening Standard.

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