Needful and penniless? Bad, I fancy (13)
I believe the answer is:
indispensable
'needful' is the definition.
(thesaurus)
'penniless? bad i fancy' is the wordplay.
'fancy' indicates an anagram.
'penniless'+'bad'+'i'='pennilessbadi'
'pennilessbadi' is an anagram of 'INDISPENSABLE'.
'and' acts as a link.
(Other definitions for indispensable that I've seen before include "Absolutely necessary" , "Vitally necessary" , "Essential" .)