So just managed to finally kill normal botanist, using the scorch tactic. Since it was usable on normal, it may also work on heroic, it basically allowed me indefinite staying power as long as I didn't mess up.
What I did was to stack movement speed items, giving me a total of 114% speed. This + scorch kiting with frenetic speed and blink is just fast enough to occasionally reset the stacks while the botanist casts a spell and during phase transitions. Additionally, because of the kiting, the bosses hit you less frequently, which reduces incoming damage and stacking speed by quite a lot. This allowed my heals to exceed the damage income, so I was sitting at near full health most of the time, while having mirror images / ice block open for emergencies.
It was pretty hard to do, and it took much longer, but it may be a good approach to heroic if a normal nuke+pray strat isn't working.
The most important thing seemed to be utilizing every opportunity to reset stacks properly, wile making sure blink is up for parasitic fetter, since that would destroy me. Luckily, it so happened that the blink on parasitic fetter if timed properly could often also often double as a stack resetter
I really don't know what's different then. If I even survive to 1:30, which is by no means guaranteed, the stack always get refreshed at around 2 secs remaining. I've yet to see it fall off a single time, after perhaps 8 or so attempts where I made it to bridge breaking. I've tried all 3 specs and hit the bridge breaking with them, but no luck. You don't happen to have some effect reducing the duration of that debuff or something, right?Nah I don't think you got lucky, it's just that on Heroic I cannot survive long enough. Searing Brand does something like twice the damage it does on Normal. On your logs you lose stacks around 1:30min (bridge breaking probably), but I don't even get that far. I usually die in less than a minute.
If I could get the stack to reset I imagine I could make it, since I'm easily outhealing the initial low stack damage.
Btw, does anyone know if legion mythic+ is still active? I was trying to get a keystone but couldn't get one to drop while soloing mythics (did halls of valor, karazhan and thicket, all of which were easy enough on level 0)
Edit: Garothi down too. He somehow bugged out while hitting enrage on the second transition and did exactly nothing afterwards, so I'm not sure if counts as legit, but I'll take it.
I found a method of essentially ensuring that you'll survive. First, as isaac suggested, don't dps during the transition, you take much less damage that way. Second, if you put you water elemental in melee range of the boss, without standing there yourself, he will melee your water elemental and not cast his carnage ability. He takes a while to kill it and you can resummon before he does. If you also avoid the fel bombardments, then you'll easily live through the encounter. Hitting the enrage ends up being the main problem.
On first glance, the hounds, the portal keeper, high command and Eonar all seem out of our league right now, but I'm gladly proven wrong. The hounds don't seem to be properly separable, with the water elemental dying rapidly. The portal keeper just hits like a truck and there doesn't seem to be a way to reset your stack. The high command stacks are resettable, but the melee swings just overpower my defenses really quickly. In eonar's encounter it's impossible to be everywhere at once, and the fel-infused destroyers in particular finish it all off really quickly while taking ages to kill