Potter character that could be total tonic (10)

I believe the answer is:

cottontail

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'potter character' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

'could be total tonic' is the wordplay.
'could be' indicates an anagram.
'total'+'tonic'='totaltonic'
'totaltonic' anagrammed gives 'COTTONTAIL'.

'that' is the link.

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I've seen this clue in The Independent.

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