TO beat the Yian Kut Ku you need to get the following items before you start the quest Slay The Great Kut Ku : stones x5, large Barrel bomb+ x2, Potions Mega if you can get them x10, Pitfall trap, felvine x10, and an iron great sword up graded to an Iron katana "grace". When you start the quest grab the items and head straight to area nine. When you get there run all the way to the end past the cats(felvine is so that the cats dont steel your items) and you will see the Kut ku. Don't attack it set the pit fall trap then get its attention with a rock. When it sees you lure it in to the trap and set both large barrel bomb's next to him. Try to get some distance and throw a rock at the barrels to set them both off. This will weeken him alot so all you have to do is attack him with your great sword. Attack it from the side hitting its soft spots(wings, head, tail)Repeatedly until dead. if he gets away head to area 4. if he gets away from there gor to area 6.