The second form is pretty tough with one of its attacks that can easily kill, even at full health. I spent alot of time grinding for throwing items and exploring some other areas so I dont have a solid completion time but I was on this boss for over 2 hours of my play time on the game. On my first attempt I came very close to beating the boss, but then it took quite a few attempts after that to get the KILL.
One of the big things that helped was stocking up on Saw Blades. Ive also been using the parry arm which has been great, but I started using that prior to this fight. The saw blades gave me that edge and allowed me to get the boss health down in his later more aggressive phase while keeping a distance. Healing the summoned character midway also helps, but this was nothing new.
My good friend CoolHandMike let me know about the shotput items which I now keep stocked. Great for setting up a critical blow on stunned bosses without having to charge a heavy attack to initate it. The saw blades work pretty well for extra damage so will use some of those items more now too. Wasnt really using any throwing items.