Someone I'm not identifying who's an absolute beast (2-3-2)

I believe the answer is:

so-and-so

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'beast' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for so-and-so that I've seen before include "Right little rascal!" , "Person unspecified or abjured" , "Person unknown or disapproved of" , "Unpleasant person - whose name has been forgotten!" , "This/that person/thing" .)

I've seen this clue in the Evening Standard.

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