As said by J-Roc on "Trailer Park Boys", a mafucka is the urban bastardization of motherfucker (q.v.) however its use can vary widely, see example:
"Game's postponed because no mafuckas can go to Canadian Mafucka and get a new orange mafucka for $2.99 !?"
by J-to-the-R-O-C August 7, 2005