Marrow is quite easy, the fight is all about reflexes. Here is the strategy:
At first, between you and him there is a spike pit and his annoying parrot attacks you (sometimes he shoots you, too, but not always). To be able to reach him, you should hit the parrot 3 times. One advice - if you hear the shhh-sound and you see something green coming, attack with sword. You may try to duck just after the attack, it will lowerr it's chances to hit you if you have missed with the attack, but it requires good timing, or you will miss due to the ducking.
Once you hit the parrot 3 times, 2 rocks appear over the spike pit. Here you jump to Marrow. The rocks are lower than the ground on which he is standing so do the following: wait for him to come close, jump (low jump), sword attack and then duck to avoid the retaliation. Repeat until you do 5-6 shits - then his parrot lifts him and you must quickly jump on his platform (the rocks under you start to dissappear) or you will die. And then you're back to Phase One. Repeat until he is dead.