I know I'm lol weeks late, but I killed Inferno Diablo today without any kind of cheesy stuff (no exploiting hydra heals, obviously no pre-nerf force armor or crit mass). So, I thought I would post a little write-up for it, in case anybody else is struggling with it.
This is the build I used.
All of the ability choices are geared around phase 2. Phase 1 and 3 are trivial.
Abilities (phase 1):
Teleport: He teleports to you and slaps you in the face. With force armor this is survivable, you can also usually pop diamond skin or teleport to get away before he swings, as the teleport itself doesn't do damage. That said, you should rarely, if ever, have this happen. He only teleports if you're standing near a map "edge" element. Not necessarily an outside edge, but the edge of any map element you can't pass through - like a crack in the ground in phase 2, or the center pits in phase 1/3.
Debuffs: He has two different DoT debuffs, both are applied in melee. If you don't let him teleport to you, you should never get these. If you do get them in phase 1/3, no big deal - the health wells don't just heal the damage they do, they also clear the DoT! If you get a DoT in phase 2 chances are you're gonna die.
Explodey fireball: Single big fireball that explodes and burns the ground, for initial damage followed by DoT damage. With force armor it shouldn't kill you, but you can usually avoid it by teleporting or just running laterally (don't run away from it, it will probably just keep going and hit you). Slow time also works well for it, you can slow it and then dodge at your leisure.
Fireball nova: Bunches of fireballs, not very dangerous. You can usually weave between them, but if not, they'll just hit you for 35% (force armor, yay) and don't have a DoT or anything bad associated. Diamond skin should full absorb assuming you don't have too many HP. These can also be stopped and dodged with slow time.
Cages: Trivial, he stops and puts black stuff on the ground. Don't stand in it. If you mess up and stand in it, you get trapped, then he teleports to you, picks you up, drains you to like 1hp and sets you down. Pop diamond skin as soon as you land and you can usually live, teleport to a health well immediately and you're okay. All the same don't get caught in this, there's no excuse for that. Note that the radius it grabs you is a little bigger than the graphic, so leave some room to be sure.
Abilities (phase 2):
All the same abilities as phase 1, except he doesn't fireball nova. Instead:
Shadow clones: They hurt. Spawn immediately, and then again when diablo is at 66% and 33%. Fortunately we have spec'd completely for dealing with them. The wizard uses a lot of abilities, most of them can be stopped by slow time. This is why we really picked up slow time.
Abilities (phase 3):
All the same abilities as phase 1, plus an additional ability:
Lightning breath attack: I have no idea how hard this hits, because it is trivially easy to avoid. Don't get hit with it, I assume. (I never did)
Strategy (phase 1):
Kite kite kite. He won't teleport to you unless you stand near an edge, so kite around the map in a circle, staying equidistant from the outside and the holes in the middle. Keep diablo just off your screen as you kite, with venom hydra down there and just toss seeker missiles, they'll find him. Keep stutter-step backing up as he comes at you. Sometimes he might charge you, if he does that teleport away and continue kiting.
This is not a DPS race, it is a survival race. Your goal isn't to do damage to Diablo. Your goal is not to take damage from diablo. Never try to get that extra cast off, just keep moving. If diablo is visible on your screen, you should be moving/teleporting, not casting anything, ever. If you **** up and get hit, teleport away, use a health potion. Don't use a health well unless you really need it. Try to keep them available in case you get a DoT and need to clear it.
Strategy (phase 2):
As let the cutscene play out so that your abilities can cool down, and your AP and HP can regenerate. As soon as you can start casting, drop a venom hydra and a slow time bubble. As soon as your shadow spawns, pop diamond skin and run until you can't see her anymore, then start spamming seeker missiles in her general direction. Her abilities will violate you if they hit you. Tornadoes, arcane orbs, venom hydras, they all hurt like hell. Drop a second slow time as soon as you're able, and pop diamond skin again as soon as you're able. Don't wait until you think you "need" them.
If it takes you a while to kill her, Diablo may come back before you are done. Don't panic, just stay away from edges and keep kiting. The edges are closer together at the bottom of the map than at the top, so the top is a better choice.
Once it is just diablo again go back to the usual kite system from phase 1, except the terrain is a little more problematic. Getting the occasional teleport is almost unavoidable in this phase, so be ready with teleport and diamond skin.
When he starts to get close to 66%/33% make sure you are at full health and have all your cooldowns before pushing him over. Repeat from the top until the phase is done.
Strategy (phase 3):
Same as phase 1. Literally nothing changes. The lightning hose isn't even a problem so long as you're kiting properly. He'll be so far away it will be a simple matter to run away when he lightning hoses at you. Again, remember, your goal isn't to do damage to Diablo, your goal is not to take damage from Diablo. If he is on your screen, you are moving/teleporting, not attacking, ever.
And that's it!