Crossword Genius

Cassandra gone trick-or-treating holding little monster (8)

Ross

I believe the answer is:

dragonet

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

'little monster' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'cassandra gone trick-or-treating' is the wordplay.
'DRAGONET' is hidden in amongst the letters.
But, I am not sure how this is indicated.

'holding' is the link.

Can you help me to learn more?

(Other definitions for dragonet that I've seen before include "spiny fish" , "Brightly coloured fish" .)

I've seen this clue in The Independent.
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