Loatheb

[Sword_of_Doom]

The killer with quicker dooms is that it tends to take out healers first, leading to gaps in the rotation on the tank, which means tanksplat in short order. You want him dead by 5:24 (just before the first 15 second Doom goes off). Sub-5 minutes is a plus, but it's really the Doom at 5:25 which will probably start killing people.
It is not, strictly speaking, necessary. That said, I was sporting Spirit of the Zandalar, Rallying Cry of the Dragonslayer, Sayge's Dark Fortune of Damage, and even Lordaeron's Blessing when I killed Loatheb for the first time. Loatheb is an absurdly stiff DPS check and every little bit helps (although I think Dire Maul would take too long).

We still prefer to get the world buffs when they're available, because of the high cost of a Loatheb pot-wipe (how much time do you really want to spend farming GSPPs?). Last kill both dragon heads were hanging and the Faire wasn't in town, so we made do with just Spirit of the Zandalar. Since the removal of the cooldown on Spirit of the Zandalar, there's really no reason not to get it, especially when it's a portal-Stormwind and a quick flight away.
This depends on your consumable rotation. Figure out what it is, then do the math for dooms and pots (assuming each shadow potion absorbs only 1950 shadow damage; any other assumption is unsafe, and yes, I've gotten a 1950 and 1953 consecutively on a Loatheb kill, so it DOES happen). Once you've gotten an idea of your consumable rotation and the damage inflicted by incoming Dooms, you'll arrive at a magic number for HP which is going to be in the ~5000 range.

In practice, everyone will exceed this amount without even changing gear. Load up on the cheap HP buffs: a Kickin' Chimaerok Chop, some Rumsey Rum, and an Elixir of Fortitude. Spirit of the Zandalar helps here too: it doesn't persist through death any more, but its +15% stats is now applied after all buffs instead of just to base stats. 15% additional stamina works wonders for survivability: low-stam healers can even use the Dark Fortune of Stamina buff instead of the Damage one if the Faire is in town.

This fight boils down to correctly managing three different rotations (perhaps they should have anagrammed "rotation" instead of "healbot"). You need a healing rotation on the MT to keep him up. You need a spore rotation to make sure all your DPS classes get the buff on time and keep up raid DPS. Finally, you need a consumable rotation that is 100% guaranteed to keep you alive until at least the 5:00 mark. Once you've gotten these things worked out, just do them in the right order at the right time for five minutes and you win.

Thanks for the reply.

We had two attempts tonight.

First attempt, we got him to 7% and everyone keeled over at the 5:10 mark.

We reloaded, 1 hour later, we killed him at the 5:30 mark. Then the remainder of the raid keeled over. What a rush, survived to the kill and then get killed by the doom.

Basically for both attempts we went with the Hakkar and Head of Ony buff and used every imaginable consumable. Used 3 Shadow pots per attempt. So i can see now why there was much complaining in the R&D forums about the cost of the consumables. We have to do that every week:( O well, fun fight and surprising small learning curve for us.