Naxxramas: Arachnid Quarter (1)

A web-covered wing of Spiders and Cultists of the Cult of the Damned. Three bosses. This is the entry level quarter, usually the first one targeted by guilds to gear up their players. The trash clear to Anub'Rekhan is short, with the clears to Grand Widow Faerlina and Maexxna being progressively longer.

Boss #1 Anub'Rekhan
10-man Abilities
-Anub'Rekhan has approximately 2,230,000 hit points.

-Anub'Rekhan Impale:
This is an area-of-effect ability that targets a random player and hits everyone in a straight line between Anub'Rekhan and the player, causing 4813 to 6187 physical damage and launching the affected players high in the air, who then suffer 50% fall damage when they hit the ground.

-Locust Swarm:
Every 70-120 seconds, Anub'Rekhan slows to 60% normal run speed and casts a spell that causes AoE damage in a 30-yard radius around him that centers around him as he moves. Remaining in the radius of effect causes a DoT debuff of 875 to 1125 nature damage every 2 seconds that stacks repeatedly, and which silences those afflicted. When he casts this spell, another Crypt Guard also spawns at his initial engage point. Lasts 16 seconds.
Notes:The Locust Swarm attack has an approximately 90-second cooldown, but the first cast may occur between 80 seconds and 2 minutes. Its silencing ability is unlike a normal silence, as it prevents the use of all abilities, even auto-attack. This means that the main tank cannot use Shield Wall or Last Stand to save himself if he gets stacked too high. Items, however, may still be used.
Aspect of the Pack can be used to get out of the Locust Swarm range but requires timing and coordination from the Main Tank and Hunter. Unholy Aura will also work if the Death knight stands a little further ahead of the kiting path and runs with the Main Tank to the initial tanking position. If you are late on your kiting and start stacking up the debuff, drink a swiftness potion.

-Summon Corpse Scarabs:
Whenever there is a corpse in the room (either a player or a Crypt Guard) Anub'Rekhan can spawn corpse scarabs from it. This is not on a set timer. Ten will be spawned from a Crypt Guard and Five from a player. They spawn with threat on random players and will spread out and attack random targets.
-Crypt Guards
One of these adds spawns after every Locust Swarm. In addition, one spawns approximately 20 seconds after Anub'Rekhan is pulled. They have around 234,000 health. They have a cleave, a stacking acid spit DoT that ticks for 500 a stack, and a low-hp frenzy that increases damage by 50% and attack speed by 60%.

-Strategy
Although doable with two tanks, three tanks are ideal for this encounter. One of them should tank Anub'Rekhan, while the others tank the Crypt Guard adds and the Scarabs that spawn from their corpses. In the 10-man encounter, the two Crypt Guards are not present at the start of the fight, making the third tank unnecessary. A hunter is helpful but unnecessary.

The main tank engages Anub'Rekhan and drags him back to where he was standing originally (note that tanking him against the wall can cause evade bugs should the tank be impaled). In the 25-man fight, the other tanks pick up their Crypt Guards while the DPS focus them down. These should be tanked and killed relatively close to Anub'Rekhan. Due to the acid DoT the Crypt Guards apply infinitely these should be killed quickly.

After this, the raid should spread out in a semi-circle around Anub'Rekhan to minimize the effects of impale. Mages should be ready near the Crypt Guard corpses to frost nova the Corpse Scarabs as they come out; the offtanks should be on or near these corpses to pick them up. Ranged DPS should focus and kill the scarabs before returning to Anub'Rekhan. You should have a decent amount of time to DPS Anub'Rekhan before the first Locust Swarm. One player—ideally a Hunter—and a healer stand 30 yards from the main tank on the edge of the room past the ring of slime. When Locust Swarm is cast, all players must immediately run from Anub'Rekhan to the other side of the room and remain more than 30 yards from him for the next 20 seconds.

The main tank, when he sees the Locust Swarm cast bar, must begin kiting Anub'Rekhan along the edge of the slime to the other side of the room. The hunter should have Aspect of the Pack on. The healer should move with them and avoid getting any stacks of Locust Swarm in order to be able to heal the tank and hunter should they be hit. A warrior tank should use Intervene to gain additional distance. Locust Swarm ends when Anub'Rekhan reaches the other side of the room, where he should be tanked as before, with the raid spreading out in a half circle. Another Crypt Guard spawns during this time; pick up and kill it. Again, Mages should be to be aware of Corpse Scarabs spawning from it. After this, the encounter continues, with Locust Swarms coming every ~90 seconds until Anub'Rekhan is dead.

-Alternate strategy (10 man version)
The kiting strategy can be difficult to master for a group with poor coordination. Ranged DPS might get caught in the swarm trying to kill the adds when the tank kites, and cause everything to go wrong. An alternative strategy is to not kite at all, but have the tank stay put and take the full damage of the swarm while the healers spam heals on him. This is entirely possible and will make the fight more of a tank-and-spank with extra healing on the swarm. Death Knights are good tanks for this tactic because they can time their damage reduction ability with the swarm and take less damage. Using Anti-Magic Shell just before Locust Swarm is cast will make you immune to the swarm for 5 seconds (7 if you have the glyph). Tanks simply have to make sure that they use their damage reduction ability before the swarm because it silences them.

Once you enter the area where Anub'Rekhan is located, have a hunter misdirect (if available) onto the main tank and pull the boss to the actual entrance doorway area and tank it there while the rest of the raid runs forward and splits into a semi-circle roughly in the center of the room. Have your secondary tank behind everyone, where the adds spawn. All ranged DPS should spread around to avoid the impale. The offtank can add some DPS or even some off-healing to the party, but be ready to pick up the adds that spawn in the back, as they can easily one-shot a cloth wearer. Once the add spawns and the offtank picks it up, all the DPS has to do is simply turn around and burn it down. Do the same when the Corpse Scarabs spawn. This tactic is meant to reduce any kind of confusion in the kiting method, so separating the boss and the add makes the fight really simple. Remember that this method only really work if your healers keep the main tank topped up, especially during the locust swarm. Due to the massive damage that tanks take from the end of a Locust Swarm, any off-healers—such as shamans or paladins—should assist in keeping the main tank alive during this phase.

Note: The adds do not hit the offtank really hard, but with a low-DPS group the damage debuff can stack and be really painful. A nice way to prevent extra damage is to stun, as this prevents them from casting the debuffs at all; these debuffs last for 10 seconds and are reapplied every 2 seconds, so if you can cast a stun (such as Hammer of Justice) when your tank has 8 seconds left on the debuff, and add one more at 2 seconds, the debuff will start to 0 again, largely reducing the damage taken. The goal is to have a chain stun ready when the elite is around 50% health to reduce the overall damage taken. The adds are undead, so the paladin undead AoE stun can work for 1 sec.
Extra Note: The small adds that spawn from the corpse are really fast and can get out of a consecrate.

From WoWwiki

Grand Widow Faerlina is the second boss of the Arachnid Quarter in Naxxramas.

10-man Abilities
Grand Widow Faerlina
She has approximately 2,230,000 hit points.

-Poison Bolt Volley:
This will hit the three closest players to Grand Widow Faerlina, used every on average every 12 to 15 seconds, but sometimes with as little as seven or eight seconds between casts. Deals 2625 to 3375 Nature damage and applies a dot that does 1480 to 1720 Nature damage every 2 seconds for eight seconds. Dispellable. Widow's Embrace prevents the use of this ability for 30 seconds.

-Rain of Fire:
Random Rains of Fire will be cast on players throughout the fight, at intervals of anywhere from six to eighteen seconds. 1750 to 2750 Fire damage every two seconds. Rain of Fire lasts six seconds. 8 yard radius.

-Frenzy:
This will be used approximately every 60–80 seconds. It will increase Grand Widow Faerlina's physical damage by 150%, her melee haste by 50% and her size by 50%. During it she will hit the tank for upwards of 15,000 damage. Widow's Embrace dispels and prevents the use of this ability for 60 seconds.
NOTE: Faerlina's Frenzy cannot be removed by hunters' Tranquilizing Shot.
NOTE: You must kill the worshipper AFTER she enrages if you want to stop her for the full 60 seconds. If you sacrifice the Worshipper before the enrage, it will merely delay the enrage for 30 seconds.

-Worshippers
There are 4 "Naxxramas Worshipper" NPCs at the start of the fight.
They will be off-tanked for most of the fight, and eventually sacrificed to Faerlina. When killed near Faerlina, they will remove and prevent Frenzy as well as silence Faerlina's nature school for 30 seconds. This fight cannot last more than 4:45 or so because there will be no way to prevent the Frenzy if all the adds are dead. It should be noted that in 10-man, the Worshippers are immune to Mind Control, and must be DPSed down. This can be tricky if your off-tank is overzealous and brings one in particular down too fast. Predetermine a kill order for the worshippers (raid marks work well), and bring one down to ~5%, then kill it once Faerlina enrages.

10-man Strategy

You will need two tanks. One tank will pick up the worshippers and offtank them right under the stairs on the left side. Any tank class is good at tanking them, as they don't deal high loads of damage. The main tank will pick up Faerlina after the OT pulls the rest and drag her to the middle of the room where everyone will spread out around her. Every DPS should focus ONLY in Faerlina, ignoring the four adds till the enrage phase is near.
The off-tank will pick all four adds, and start DPSing one of them: the one who must be killed in order to stop Faerlina's enrage.

When the frenzy is about to come off cooldown (10 secs or so) every DPS should stop all DPS and switch target to the worshipper marked to kill. Do not start attacking it, just target it and be in range for attacks. The main tank should go where the OT is, the closer the better, taking Faerlina with him. The Offtank should have lowered the worshipper's health to 15% or less.

When the enrage is up, all DPS should burst their CD to insta-kill the worshipper. If done properly Faerlina's enrage should fade, and MT can move Faerlina back to the center of the room, where DPS can resume on her.
Rinse & Repeat every time the enrage timer is close.
NOTE: Off-Tank should stop DPS worshippers at some time, because he/she will kill them all otherwise.

From WoWwiki

Maexxna is the third boss of the Arachnid Quarter in Naxxramas.

10-man Abilities
Maexxna has approximately 2,510,000 hit points.

-Web Wrap:
Cast at the 20 second mark, and then every 40 seconds after that. Sends one player flying towards the webs on the Western side of the wall, encasing them in a cocoon and incapacitating them. This ability sends the player to the same place all the time, and therefore positioning the DPS where the cocoons will spawn makes for much easier destruction of the cocoon. When encased, 2475 to 3025 Nature damage is done every 2 seconds. The cocoon, which is called "Web Wrap" and has about 6,000 health, can be destroyed from the outside.

-Web Spray:
Cast every 40 seconds incapacitating everyone in the room including the tank for 6 seconds, dealing 1750 to 2250 Nature damage. This ability cannot be resisted, and the only way to avoid it is to be dead, have Flask of Petrification, have Divine Intervention, or be already incapacitated by Web Wrap.

-Poison Shock:
Inflicts 3500 to 4500 Nature damage in a 15 yard frontal cone in front of Maexxna every 10 seconds.

-Necrotic Poison:
Reduces healing taken by 75% for 30 seconds. This needs to be cleansed immediately, Abolish Poison being the most effective way to remove it during the Web Spray. Applied to targets in melee range in front of Maexxna, generally the tank.

-Frenzy:
At 30% health, Maexxna will go into a killing frenzy that cannot be removed. Increases physical damage by 50%, melee haste by 50% and size by 15%.

-Maexxna Spiderlings - 8 Small spiders are spawned at the 30 second mark, and then every 40 seconds after that. These hit for about 1,000 on cloth and have about 7,300 HP.

-Strategy
This is a quick encounter that will be over in 2-3 minutes and hinges almost entirely on keeping the tank alive through web spray. You will need one tank. The tank should pull Maexxna near a wall and face her towards the centre of the room, the raid should position themselves behind Maexxna. Ranged DPS classes will be on killing cocoons. At the 30 second mark Mages will need to be on top of Maexxna to frost nova the Maexxna spiderlings. At this point the raid needs to AoE them down within 10 seconds before Web Spray. If any are left alive it is likely they will kill someone during it as they attack very quickly. Healers will need to apply abolish poison and all of their heal over time effects on the tank just before Web Spray. It is advisable to stop DPS at ~33% and wait for a Web Spray then blow all cooldowns to kill Maexxna so that she never does a Web Spray while frenzied which will likely kill the tank.

Lockout: Anyone not in the room when the fight begins is locked out.

Web Wrap: There are two fixed positions where the one wrapped player per application of the ability is thrown, but it alternates back and forth between both spots as new players are wrapped.

From WoWwiki (I feel its incomplete)