Majordomo Staghelm! Finally we get to pay him back for the countless bundles of Morrowgrain we collected on his behalf. The traitor! I didn't even play until Wrath, but I was adamant about doing every quest I was offered, so I too collected waaaaay too much of the stuff until I was told there was really no reason. Fun fact: I thought his name was Stranglehelm for a good year or so.
There are 4 distinct mechanics you will need to worry about in this fight.
1. Scorpion Phase. This will be your opening phase, and will start with everyone stacked up in the middle, in FRONT of the boss. The reason we all sit up front is to share the damage from his cleave. During scorpion phases it is all damage cooldowns, all the time.
1a. Eventually Domo's stacks of Adrenaline get too high and he's insta-cleaving the raid. At this point the raid spreads out to trigger the next phase. Even though we are melee, I suggest hurtling yourself out from the boss as well during this transition. If the transition is triggered too slowly Domo could get another cleave off, killing the tank and whatever melee are left.
2. Cat Phase. In kitty form Domo will leap onto various ranged raid members and leave giant fire pools on the floor. Don't worry about them, as you should be sticking squarely in the middle (having run back in after ensuring a good transition). On every leap fire cat adds are summoned and picked up by the tank. It is melee's job to kill them ASAP.All melee need to switch to the adds, period. Just like with the scorpion, Adrenaline stacks will build and Domo will leap quicker and quicker, meaning you can easily have two adds up at once before transition. If not all melee are on the ball, you might end up with three or four, overwhelming your tank.
2a.Everyone runs back in, triggering Domo's brief human form during which he will stun you and casting Searing Seeds on everyone in the raid. Make sure debuffs on you are easy to see. The debuff timer could say anything from 5 seconds to 55 seconds. At 5 seconds run out of the raid, and not towards anyone else running out or in. At 1 second pop shammy rage, the seed will explode, then you run back in to help eat cleaves with the rest of the group. If you explode you seed in group, you will wipe the raid. End of story.
Burning Orbs, which look a lot like orange alien plant pods. In 25 melee usually don't worry about these. In 10m one of the orbs might show up in the middle and then it's like Baelroc. You take orb damage for as long as you can then switch with someone else.
Tip: We find the Burning Orbs cat phase really hard on the healers, so we usually only go to 4 stacks and then switch back to scorpion. At this point flaming sycthe cleaves hit really hard but we usually only have about 15% to 10% to go. If you have a priest healer or a paladin tank you can have the tank run through the boss and eat one cleave solo. This is because both these classes have an ability that also for the tank to basically be saved from a killing blow. Just make sure the tank runs through Domo, and doesn't just try to turn him. This boss turns at the speed of molasses. A normal turn will just result in taking half the melee out.
All in all, I find Domo a lot easier than a boss like Lord Ryoltih, because this fight just requires good situational awareness, there are no random elements involved. As long as you understand the phases it's a cinch. Though I will admit this fight does require a high level of personal responsibility, especially with searing seeds.