Most mischievous revolutionary's limited in skill (7)

'most mischievous' is the definition.
(arch can mean mischievous or playful)

'revolutionary's limited in skill' is the wordplay.
'revolutionary's' becomes 'che's' (Che Guevara the Marxist revolutionary).
'limited in' indicates putting letters inside (outside letters limit or restrain others).
'skill' becomes 'art' (both can mean a talent).
'ches' placed into 'art' is 'ARCHEST'.