I'm sure that most of you have seen the nerfs that are going to hit Inferno difficulty in patch 1.0.3. When I read that it motivated me to stop farming Act 2 goblins, and doing Siegebreaker runs, and to instead focus on clearing out the rest of Act 4. When I last was progressing I had just killed Iskatu and hit up the checkpoint right afterwards. I did not want to cheat and get the waypoint from anyone so I repaired my gear, hired my good friend Kormac, and headed to heaven to beat back the minions of hell.
So I gave this guy a couple shots using my standard Splinters build. It didn't go so well because I couldn't quite dps him down fast enough even with Slam Dance. I hate to admit it, but if you look at the above link I specced Vision Quest Zombie Bears because I couldn't think of any other way.
It is important to run up towards Rakanoth at the start of the fight. I tried not doing this and he just charges you right off the bat. It's important that you don't waste Spirit Vessel when Rakanoth is at 100%. One you see him walk towards you run in to the little nook on the right side of the stuff blocking the way out. Turn towards Rakanoth and pop Big Bad Voodoo and Fetish Army and just Bears him until he dies. Ideally your Spirit Vessel will eat the charge. I used my Spirit Walk at 25% and finished him off. With this method it was actually pretty easy.
I probably wiped to Izual the most out of the three Act 4 bosses. I tried my standard Splinters build, which did more than enough damage for the fight, but I couldn't survive in that spec. The room-wide freeze attack would proc Spirit Vessel, and Spirit Walk could not avoid it. I tried kiting him until Spirit Vessel cooled off, but Tyrael kept pushing him to the second freeze.
You may have noticed a rather unconventional build. Well, I just so happened to get a nice rare Sacred Shield with all resist and intelligence on it. I put that on, and before he would freeze I would summon my Zombie Dogs, and Horrify for the armor buff, and I was able to take the hit. A few tries I ran in to the problem of living through the room-wide freeze, but getting stuck on top of a regular freeze and proccing Spirit Vessel anyways. Once I made it past the first freeze I went full burn on him, and it was no problem.
So strangely enough I wiped less on Diablo than I did on the other two bosses. I think Diablo took me about 6 or 7 tries. I never died in phase 1, and the first time I made it to phase 3 I won.
Simple phase. As long as you don't walk near any of the edges in the room Diablo will not use his teleport. This include the outer edge of the room as well as the edges around the crystals in the middle. If you avoid these he will not teleport and you then do not have to deal with getting melee'd by him. Once you take away his port the rest is easy. Keep Haunt up when you can, but don't put Diablo on screen. You want him off screen, and you want to use the mini map to aim your Splinters at him. Get him close to 50% and you will transition.
This is where all of my wipes happened. This phase is the reason why I picked up Grasp, Hex, and Horrify. As soon as the phase starts Diablo will spawn a clone of you. This happens again at 66%, and 33%. When the clone appears use Hex immediately, drop a Grasp on him, and start using Splinters. When he comes out of Hex for the first time use Horrify. He shouldn't go anywhere because he's standing in Grasp. He should get Hexed again, and then be dead. Spirit Walk if you see fit to survive.
Remember what I said about teleporting and edges? Well it's true in phase 2 as well, but it's a lot harder to move around since the room isn't shaped like a giant circle. You cannot touch the edge of the cracks in the middle of the room, the small cracks that come out of them, or the edges of the room. I did this on accident a few times, and you can generally Spirit Walk out of his melee before it hits you. I actually procced Spirit Vessel when I got careless at 20% in phase 2 and had to play super careful. Let the cinematic cut-ins play out if you need Spirit Vessel to cool down.
So the main difference between this and phase 1 are that your heart rate is probably super elevated from getting out of phase 2, and he does a giant breath attack. If you are keeping him off screen like you did in phase 1 then the breath will not even be an issue. I never even saw him do it, but I could hear him doing it. Keep your cool in this phase, and don't take any risks. Do damage when you can, and when you get him a bit below 10% you win. I tried to spam my screenshot button, but apparently I didn't get any of the screenshots.
Here's a picture of my stats that I had through the whole act. It certainly helped make the fight quicker, which allows for less mistakes, but it's certainly not needed to have this much damage. As long as you are avoiding the edges and doing safe damage it should be no problem. I would wager that a Wizard could employ this strategy using Hydra and Magic Missile and do just fine. Let me know if you guys have any questions.