Hey guys. Im not raiding much for some time now, but i still pug occasionaly.
Last week i got a pug trying Heroic magmaw for the first time and wanted to see if you guys use CDs in a similar way i tried. I was using bubble/my HoP/healers Hop on mangles, and using normal mitigation cds for tanking mag when i had the 50% armor debuff.
Im currently at 175K-ish hp raidbuffed and 92% table coverage, im sure it isint any itemization issue.
Just a clarification, i wasent "omg unhealable" (though i did die once to a hit-mangle in succession - since im only HoPing after he chews me up, i was taking the first spike from mangle unmitigated), just was alot more spike damage then i expected. More then what i felt in heroic halfus, for example.
Use divine protection about 7 seconds before each mangle to soften the effect of mangle + an errant melee swing. I have specced so I have a 3 minute cooldown on HoP, so between me, the retri and the holy paladin there is always a HoP ready. Make sure you have Guardian ready for the final push under 15%, the healers have enough going on to worry about you what with all those shadow bolts flying around.
You don't want to tank magmaw with the armor debuff on heroic. After you get mangled you pick up the big adds from the OT and he tanks magmaw next. As warrior i use shieldwall a few secs before mangle hits and use last stand whenever i drop low, mirror use is also nice to mitigate some of the lava spew damage.
It's probably not optimal to be tanking Magmaw with the debuff (as mentioned above) but we've done it that way anyway. I wear my 4pc Tier for this fight so GAnK covers nearly all of one "phase", and it's up for every second one. When it's not available, AD+DP, followed by trinket when they expire.
The damage with sweltering armor really isn't that high
You shouldn't underestimate his hitpoints, he's only rockin' at 175k. 92% ctc is neat but there might happen some back to back unmitigated hits once in a while. We swapped tanks for the firstkill but stopped sometimes afterwards because it just wasn't needed, only popping CD's for mangle (including the initial tick).
For starting heroic raids (or real "progress" in general) you might want to up your hitpoints instead of covering as much of the combattable as possible, your healers will have to work harder but there's more leeway for errors.