Waiting for you deep in the Heart of Sin is the Lord it himself. He’s a tough foe with a wide variety of devastating attacks. He shoots a slow moving fireball that will chase a player for a short time. Run away and dodge as soon as you see it coming as the molten ball packs a punch. The fireball is pretty slow, so evasion shouldn’t be that difficult.
One of his most deadly moves is his ability to create fields of poison on the ground. These dark pools are huge and Azmodan covers most of the battlefield with them. Try to stay moving and outside of their reach as they can quickly kill you. Fortunately the pools don't last long and will eventually clear off the map.
His last two attacks are much weaker and even easier to dodge. Azmodan rains corpses from the sky in a circular area but this kill zone can easily be spotted by the large red ring on the floor. His final attack is a beam similar to the Wizard’s Disintegrate. You should simply run away from the beam. All characters will be great during this battle and Azmodan isn't as physically tough as his brothers, so his health should fall quicker. Just hammer on the damage and keep an eye out for what he is casting and you will do fine against this sinful monster.
Rakanoth is a demon out to cause some serious despair. He’s a tough fighter that will close in on you and hit you for a ton of damage. The fight itself is rather simple. He occasionally summons a few minions but they are weak and easily dispatched.
Most of the time, he will personally try to hit you with his large hand-swords by either walking to you or teleporting. His teleport attack can be vicious and on weaker characters it could cost you your life. Sadly it is also very quick and you’ll dodge it by luck for the most part. Other than his teleport the fight is rather straightforward. Melee people might have to kite him if he eats through too much health, but ranged characters should be able to simply hit-and-run to victory.