Frank is one hell of a b*tch
You have to let him draw close to you and as soon as you can slash him with your chainsaw,then he'll probably get ready to punch you, then you have to watch what he's doing, most of the times you'll just want to jump out of the way(you have time enough to run away safely since frank isn't one of the fastest guys), but when he's going to wipe the floor you should just stay still and when the game says so you have to swing your wii mote down, this will deal a great amount of damage...
just repeat this untill you kill him( You should have at least 1 credit , you can get an extra credit somewhere in the stage so if you don't die you can get to frank with 3 credits, you probably won't use them all anyway, but it's good to have them)