Mischief and deadpan gags having malign influence (7)
I believe the answer is:
devilry
'mischief' is the definition.
('devilry' can be a synonym of 'mischief')
'deadpan gags having malign influence' is the wordplay.
'deadpan' becomes 'dry'.
'gags' means one lot of letters goes inside another.
'having malign influence' becomes 'evil'.
'dry' enclosing 'evil' is 'DEVILRY'.
'and' is the link.
(Other definitions for devilry that I've seen before include "reckless mischief?" , "Wicked activity" , "It's sheer malice" , "wickedness" , "wicked behaviour" .)