I challenge MO used for an artist (12)
I believe the answer is:
michelangelo
'an artist' is the definition.
(Michelangelo is an example)
'i challenge mo used' is the wordplay.
'used' indicates anagramming the letters.
'i'+'challenge'+'mo'='ichallengemo'
'ichallengemo' with letters rearranged gives 'MICHELANGELO'.
'for' is the link.
(Other definitions for michelangelo that I've seen before include "Florentine painter and sculptor" , "Sistine ceiling painter" , "Famous sculptor" , "genius" , "Italian sculptor (David)" .)