Who might ridicule heartless Costa Rica sightseer losing ring (12)
I believe the answer is:
caricaturist
'who might ridicule heartless costa' is the definition.
I can't judge whether this defines the answer.
'rica sightseer losing ring' is the wordplay.
'rica' becomes 'carica' (I can't explain this - if you can you should believe this answer much more).
'sightseer' becomes 'tourist' (someone visiting certain sights).
'losing' indicates named letters should be taken away.
'ring' becomes 'O' (letter resembling a ring).
'tourist' with 'o' taken away is 'turist'.
'carica'+'turist'='CARICATURIST'
Can you help me to learn more?
(Other definitions for caricaturist that I've seen before include "Comic cartoonist" , "Steve Bell, for example" , "USA art critic (anag)" , "Artist producing comic portraits" , "Job sketching exaggerated facial features" .)