The devil is, I'm a poor starter! (3)
I believe the answer is:
imp
'the devil' is the definition.
(devilish creature)
'i'm a poor starter' is the wordplay.
'i'm' becomes 'im' ().
'starter' indicates taking the first letters.
The initial letter of 'poor' is 'p'.
'im'+'p'='IMP'
'is' is the link.
(Other definitions for imp that I've seen before include "Rascal" , "Minx" , "Mischievous creature" , "A small mischievous devil" , "Emperor" .)