Mutant regent's nip is showing (10)
I believe the answer is:
presenting
'showing' is the definition.
('present' can be a synonym of 'show')
'mutant regent's nip' is the wordplay.
'mutant' is an anagram indicator.
'regents'+'nip'='regentsnip'
'regentsnip' is an anagram of 'PRESENTING'.
'is' acts as a link.
(Other definitions for presenting that I've seen before include "job in TV" , "putting on a show" .)