Pleasant individual's congratulations (4,3)
I believe the answer is:
nice one
'congratulations' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'pleasant individual's' is the wordplay.
'pleasant' becomes 'nice' (associated in meaning).
'individual' becomes 'one' (an individual is one person).
'nice'+'one'='NICE ONE'
Can you help me to learn more?
(Other definitions for nice one that I've seen before include "Congratulatory phrase" , "very good" , "like it!" .)