The start of the fight sees the two shaman, Earthbreaker Haromm and Wavebinder Kardris, who share a health pool, inside what used to be Garrosh's throne room. They are accompanied by two dogs, and the room is extremely small for the fight on 10-man difficulty, let alone 25-man, so it is best that all four are pulled outside. On PTR, the pull required quite some caution, as the combination of a +100% frost damage debuff cast on the Haromm tank and Kardris' Froststorm Bolt caused some serious issues if aggro was not well-managed, not to mention the bolt one-shotting DPS and healers. The two wolves seemed completely insignificant, with only 12 million HP each they were DPS'd down extremely quickly, then the fight begins for real.
Just like any shaman, these bosses' abilities revolve around the summoning of totems. There are three totems, which are placed at 90%, 80% and 70% health, and give each boss different abilities. These totems really are the key to the fight, as with the exception of the two frost abilities mentioned before, the bosses really don't do a great deal that isn't related to the totems.
This is the first totem to appear, when the bosses' joint health pool reaches 90%, and grants the two bosses two abilities. Firstly, Earthbreaker Haromm will be granted Toxic Mist, which seemed to debuff two players at a time, not only inflicting a reasonable 120,000 nature damage per three seconds, but also applying stacks of Toxicity, which was far more problematic, as it stacked up, increasing nature damage taken but 10% per stack. We didn't see it stacking up above 5 stacks, but in a fight where pretty much all the damage is nature damage, +50% is a big deal. The good news is that the majority of the damage is avoidable, but obviously this debuff makes any misstep a far bigger issue. I wouldn't be surprised to see this nerfed somewhat before this encounter goes live.
This is the second totem to be summoned, when the bosses' joint health reaches 80%. Earthbreaker Haromm is given Foul Stream, which appears to fixate on a single player, then flash a broad line of liquid onto the floor, which lasts a short while before disappearing. Again, this inflicts nature damage, and a lot of it, 300,000 to be precise. Don't stand in it! It really does disappear very quickly, the only screenshot I was able to get of it is the one in the header image at the top of the article.
This totem is the last of the three to appear, when the shamans' health pool reaches 70%. Of the totems, it seems to be, mercifully, the least troublesome of the totems. It gives Earthbreaker Haromm, for once, the more entertaining ability, Ashen Wall. This wall of elementals will deal damage to anyone near enough to it to be in their range, but on the PTR, it seemed that they had come over all Gallic and gone on strike. They did almost no damage, and we couldn't find anything in the combat logs indicating that they were doing anything at all. They look cool, though.
Yes, they really are shaman! The fight continues to revolve around these three totems and their associated abilities, until the shamans' health reaches 30%, when they will Bloodlust, increasing all their damage dealt by 30%, and their haste by 30%. While it isn't 100% confirmed to be the case, it would be odd indeed if this didn't include all the summoned abilities, as the shamans themselves really don't do a great deal.
Obviously, this fight involves a good deal of kiting, and as such is not ideal for melee DPS. Haromm is probably the best primary target, as they share a health pool, and Kadris has this annoying habit of constantly summoning things on her head. All the really troublesome abilities come from Kadris, so it could be viable to take Haromm somewhere quiet, like inside a building, and DPS him down while leaving a smaller party outside to deal with Kadris. Of course, this is PTR, so everything's subject to change!