Fight is split into a number of phases
At the start of the fight, Darkfang and Bloodclaw should be picked up and killed asap we then move onto the 2 main bosses who share a healthpool.100 - 80%
Haromm begins casting Toxic Mist on random raid members. The healers have to respond to this ability by doing extra healing on affected players.
Kardris begins casting Toxic Storm, and summoning Toxic Tornadoes. Since these move around, your raid members will have to always be aware of their surroundings, and they will have to avoid them at all times. As the fight goes on, the number of tornadoes present will increase, causing your raid to have less and less space. This acts a soft enrage timer.80 - 70%
At 80% health, Haromm begins casting Foul Stream Icon Foul Stream. This ability deals very high damage to any players it hits.
Kardris begins casting Foul Geyser Icon Foul Geyser at 80% health. This ability is the most problematic one in the entire fight. The resulting Foul Slimes cannot be tanked in melee range due to their very high damage aura present within 3 yards of them, so they will need to be kited. Tanks who can reliably generate solid threat at range, so Brewmaster Monks, are good for this task. Alternatively, you could have them kited around by a ranged DPS player, such as a Hunter or a Mage.70 - 25%
Haromm begins casting Ashen Wall Icon Ashen Wall. Like with most of the other abilities in this fight, players will simply have to immediately move away from where the wall is placed.
Kardris begins casting Falling Ash Icon Falling Ash at 70% health, and this ability is very easy to deal with. Players have around 30 seconds to make sure that they are not standing within the marked area on the ground, which is more than enough time. When the fiery projectile of the ability lands, the entire raid will take a moderate amount of Fire damage for which the healers must be prepared.25% down
When the bosses reach 25% health, their damage increases by 25%. This part of the fight will be the most difficult one, because your raid will be running low on space (due to the Ashen Wall Icon Ashen Walls and the increasing number of Toxic Storm Icon Toxic Storm clouds) and probably also on mana. Defensive cooldowns are best used here. Basically nuke heroism, cd phase while dodging stuff.