Serpentshrine Cavern

Serpentshrine Cavern is the raid wing of Coilfang Reservoir, where Lady Vashj has made her lair. It is a 25-man raid instance with six bosses, culminating with Lady Vashj herself. There is no longer an attunement required to enter this instance.

For most raids, Serpentshrine Cavern will come only after the raid has been farming Karazhan as well as Gruul's Lair.

* Tokens for Tier 5 gloves, legs, and helms drop in the Serpentshrine Cavern.
* Lady Vashj, the last boss, drops the second quest item needed to be attuned to Mount Hyjal: Vashj's Vial Remnant. The quest can be found here: The Vials of Eternity
* In an interesting twist The Lurker Below must be fished out of his pool rather than pulled.
* There is no required boss order in this zone, as there are several paths from the zone-in to Lady Vashj. The main 'cavern' is composed of a collection of large bridges and platforms above water. By using waterwalking you can start pretty much anywhere. Creative mechanics will be needed to begin waterwalking so you don't break the water when you jump down onto it (paladin bubbles, Slow Fall, etc...).

NPC Respawn Timer

Respawn timer for all trash groups is 2 hours. If their related boss is defeated, they will not respawn.

The water

* Coilfang Frenzy are fish that attack anyone who enters the water, to prevent skipping areas. The longer you are in the water, the more fish spawn. They will despawn once you are out of the water or dead. Once The Lurker Below is defeated, these will no longer spawn. Any forms of waterwalk (i.e. priest's Levitation) prevent the mobs from attacking.

Scalding Water

As long as the 6 platform packs surrounding The Lurker Below are cleared, the water will be boiling, killing all of the Coilfang Frenzy in the water. Entering the water during this condition results in a Scalding Water debuff, which inflicts 500 damage every 3 seconds (avoidable by using any forms of waterwalk). This is considerably less damage than attacks from the Coilfang Frenzy. If the platform packs respawn, the water stops boiling and the Coilfang Frenzy return.

Defeating The Lurker Below prevents both the Scalding Water and the Coilfang Frenzy, allowing more convenient navigation of the instance.

NPCs related to Hydross the Unstable

Once Hydross the Unstable is killed these will no longer spawn.

Pack type 1

This is the first type of pack you'll encounter as you enter. There are about 3 of these packs before Hydross the Unstable. 5 tanking classes of some sort can be used, although the Serpentshrine Sporebats can be CC'd when not enraged. Tank the Coilfang Hate-Screamers away from the group to prevent silence. Burn the Coilfang Beast-Tamer while his Serpentshrine Sporebats are tanked (they randomly charge). Once the Coilfang Beast-Tamer is dead, the Serpentshrine Sporebats will lose their enrage, at which time they can be Crowd Controlled. Burn the Coilfang Hate-Screamers and then finish off the bats at your leisure.

Note: If the Serpentshrine Sporebats are sheeped far enough away from the Coilfang Beast-Tamer, occasionally they do not become enraged and break sheep.

* [71 Elite] Coilfang Beast-Tamer x 1
* [71 Elite] Coilfang Hate-Screamer x 2
* [71 Elite] Serpentshrine Sporebat x 2

Underbog Colossus

[72 Elite] Underbog Colossus appear as single pulls between each of the Pack type 1's. Although their abilities can require some thought, they are relatively easy. Nature resist gear helps.
Platform around Hydross the Unstable

These mobs move around Hydross the Unstable's platform Tainted Water Elementals come from the right and stop in front of Hydross the Unstable and become Purified Water Elemental then continue along the platform. They have relatively low hit points but a huge aggro range.

[71 Elite] Tainted Water Elemental
[71 Elite] Purified Water Elemental
Hydross the Unstable encounter

During the encounter when Hydross the Unstable changes form he will spawn 4 adds. Tainted Spawn of Hydross for poison form or Pure Spawn of Hydross for water from.

[71 Elite] Tainted Spawn of Hydross
[71 Elite] Pure Spawn of Hydross

More at wowwiki.com

For those at max level soloing [zone=3607] and unfamiliar with the raid:

The final boss ([npc=21212]) will become invulnerable for phase 2 (70% hp).
During this phase [npc=22009] will spawn every 30/45 seconds. You can spot them from the green poison they shoot at you.
Kill and loot them to obtain [item=31088] which will allow you to deactivate each of the 4 orbs.
Once this is complete [npc=21212] is no longer invulnerable.

No idea if this is intentional or not but ... Lady Vashj dropped https://www.wowhead.com/achievement=694/serpentshrine-cavern#a Helm of the Vanquished Hero and a Helm of the Vanquished Defender token.
I mailed one to my hunter and one to my priest.

Upon using the token they both got this achievement although neither one of them ever set one foot in Serpent Shrine Cavern.

Weird...