Crossword Genius

Curtail activities, but complete self-portrait as a Devil? (4,2,4,5)

Ross

I believe the answer is:

draw in ones horns

I'm a little stuck... Click here to teach me more about this clue!

'a devil?' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'curtail activities but complete self-portrait as' is the wordplay.
I cannot quite understand how this works, but
'complete' could be 'one' (I've seen this in another clue) and 'one' is found in the answer.
'as' could be 'in' (I've seen this in other clues) and 'in' is found within the answer.
'activities' could be 'draws' (draw is a kind of activity) and 'draws' is found within the remaining letters.
The remaining letters 'horns' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for draw in ones horns that I've seen before include "finish self-portrait as a bit of a devil?" , "Economise" , "save" , "Cut back" , "Scale down ambition" .)

I've seen this clue in The Guardian.
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