Ghom is the first true boss in Act III of Diablo III. He’s a fairly simple boss to face, but he’s also pretty nasty- both in terms of his theme and in terms of his fight.
Basically a huge four-legged lump of lard with an excess of mouths, Ghom closely fits the theme of Azmodan’s other minions- large and stompy things that may not be the fastest around, but dish out serious hits and are overall excellent siege machines. In Ghom’s case, this is accomplished with only two special attacks- there’s just a lot of power in Ghom himself.
The first and most obvious of Ghom’s special attacks is his noxious farts. No you’re not reading that wrong. Periodically during his fight, he will stop for a couple of seconds and shake in place, emanating a putrescent-brown smog of noxious gas. This gas is very damaging, and covers a rather large area- don’t stand in it if you can help it. Melee artists like the Barbarian and Monk will need to either find a way to function at range (unlikely) or set themselves up with skills that can reduce the damage or make up for it with constant healing (vastly more likely).
Ghom’s other special attack is his sole ranged option- he horks up a pair of lemon-yellow slimes and projectile-vomits them at you. While these little things are annoying, they aren’t terribly harmful, and actually expire after a certain amount of time.
Because of this, ranged combatants have a really easy time dealing with Ghom- just kiting him slowly in a circle around the outer edge of his arena will give plenty of space to avoid his gas and slimes, and you can keep pumping ranged attacks into him until he dies. Melee combatants have a much harder time, but don’t have to worry about the bile-slime, since he won’t use it on a target standing next to him.
Being one of the very few boss fights that you can find yourself in without any adds popping up, single-target attacks are unquestionably the way to go with Ghom; forget all your area business and stick to whatever will destroy one target as fast as you can. Make sure you’ve got whatever healing skills you can if you’re melee; Barbarians will want to power up health orbs pretty hard and pick up any life-leech runes and items they’ve got. Monks the same, but with the skill that causes Spirit use to heal them.
Curiously, Ghom’s achievement (Crop Dusting) requires not standing in his gas, which is pretty much the way to fight him as a ranged character, so expect to pick that up the first time you fight him with anyone that likes standing at a distance anyhow.