Seasonal visitors beginning to congregate? Very good (5)
I believe the answer is:
magic
'very good' is the definition.
'seasonal visitors beginning to congregate?' is the wordplay.
'seasonal visitors' becomes 'magi' (the Magi or wise men who visited Jesus).
'beginning to' suggests taking the first letters.
The first letter of 'congregate' is 'c'.
'magi'+'c'='MAGIC'
(Other definitions for magic that I've seen before include "Mysterious quality" , "Spelling?" , "Entertainment at a children's party?" , "'Charms, spells, illusions (5)'" , "Tricks" .)