Karazhan Tactics - Woulda been useful in the past.

Well since someone got lazy, I'll do the honours (I asked, honest! D:)

I'll tackle the bosses in order, starting with:

Attumen the Huntsman and Midnight
This is an optional boss.
Before this encounter starts, Midnight will be standing alone in the stables, waiting patiently for you to tackle him, he is neutral to the group and can be skipped.
The encounter starts when Midnight is attacked, and is fairly much tank and spank
After 2% damage to Midnight is done, Attumen will spawn, who will probably go straight for the healer and should be picked up by the tank, the group should continue to focus on Midnight.
During this time, Attumen will cast a curse occasionally, reducing the chance to hit by 50% for everyone affected. Should be dispelled by the mages/druids.
When either Midnight's or Attumen's HP drops to 25%, Attumen will mount Midnight, restoring all HP, the encounter will continue as it was, only now Attumen will charge at random people, knocking them back.
Continue DPSing Attumen and claim lootz, yay!
"Come Midnight, let's disperse this petty rabble!"

Moroes
This is a required boss.
Moroes will be spawned in the Banquet Hall of Karazhan, quite near the Stables and is a required encounter in order to progress, since without killing him, you canot proceed to the Opera Event, or Curator. the room should be cleared of all mobs prior to engaging Moroes (Current TW aggro range may cause moroes to aggro if you pull a mob too close to him, efficiently whiping the group).
Moroes has 4 (randomly selected out of 6) adds, which should be taken down before Moroes, in this order:
Baroness Dorothea Millstipe (Burns Mana)
Lady Catriona Von'Indi (Heals)
Lady Keira Berrybuck (Heals and Bubbles self)
Lord Robin Daris (Cleaves)
Baron Rafe Dreuger (Bubbles self)
Lord Crispin Ference (Shield Wall)
During the battle, Moroes will occassionally stealth, and Garrote a random party member upon unstealthing, at 20% HP he will enrage, increasing damage by 20%, he will no longer stealth while enraged.
"One more for dinner this evening."

Maiden of Virtue
This is an optional boss.
The Maiden of Virtue will be spawned in the Guest Chambers of Karazhan and has no adds.
The Maiden should be tanked in the center of the room, where she stands, with all ranged dps outside the shrine.
One of the healers should be hiding behind a pillar, out of line of sight, healing ranged only.
She will use a Holy Ground effect that will silence everyone within 10 yards for 0.5 seconds every second.
Every once in a while, the Maiden will cast Holy Wrath, which works much like a Chain Lightning, hitting the first target for roughly 2k, then 3k, 4k on the next target, and 5k on the last.(*BUG* CAN HIT FOR 20K!)
Lastly, she will use an all-party Repentance, stunning everyone for 10 seconds, this is where the hiding healer comes out and keeps the main tank alive, when Repentance fades, he will go back to hiding.
"Your behavior will not be tolerated."

Opera Event
This is a required boss.
Starts when you speak with Barnes.
Can be either one of the following three:

• Big Bad Wolf: Fairly easy fight, may fear nearby players, if you get turned into Red Riding Hood (Gnome), run away from him.
  
• The Wizard of Oz: Consists of 5 bosses which should be tackled in the following order,
  
  • Dorothee (AoE fear, no aggro table, kill BEFORE Tito),
    
  • Roar (AoE fear),
    
  • Tinhead (Use frost spells to slow him considerably),
    
  • Strawman (Use fire spells to occasionally stun him).
    
  • When they are all dead, The Crone will spawn, tank n spank for loot.
  
  
• Romulo and Julliet: Currently bugged, will be updated when it's fixed

"Welcome, ladies and gentlemen, to this evening's presentation!"

The Curator
The is a required boss, killing him will allow you to use the backdoor (yes I know it's bugged and always open @.@)
Try to clear as much of the room as possible before starting, this encounter will consist of 2 phases, firstly the "Spawning" phase, and secondly the "Evocation" phase
During the Spawning phase, the Curator will spawn Astral Sparks (10 in total), which should be killed as soon as possible, each will take 10% of the Curator's mana.
The Evocation phase will start when the Curator goes OOM, restoring 5% mana per second, during this phase he will take 200% damage so you SHOULD DPS him during this time.
The Curator occasionally targets the second person on his aggro list with an Hateful Bolt.
At 15% HP, he will enrage. This largely increases melee damage output and rate at which Hateful Bolts are cast. It will not summon Astral Flares or use Evocation during this time.
If the Curator is not killed within 12 minutes, it will go berserk and end the raid quickly.
"Do not touch the displays."

Terestian Illhoof and Kil'rek
This is an optional boss.
During this battle, Kil'rek the imp should be killed as fast as possible, on death he'll debuff Terestian, increasing the damage Terestian takes by 25% for the remainder of the fight.
After a short amount of time, Terestian will open two portals, which will continiously spawn imps which should be AoE'd down or they'll herass the healers.
Over the entire battle, Teresting sacrifices people, chaining them in Demon Chains in the center of the room, these should be destroyed AS SOON AS POSSIBLE, Terestian is healed for a % over 100 the damage done, and if left too long, the sacrificed player will die.
After 10 minutes, Terestian goes into a rage, and begins to spam shadowbolts that hit for 7,000 damage on the entire raid.
"Let the sacrifice serve his testament to my fealty."

Shade of Aran
This is an optional boss, killing him will allow you to Teleport to his former location from the main entrance by talking to Berthold.
Shade of Aran has no aggro table and cannot be tanked, instead, he will cast Fireballs, Frostbolts and Arcane Missiles at random targets, he will also cast Blizzard which atm only slows movement speed, if there's a Warlock in the group, (s)he should keep Curse of Tongues on Aran.
He will often cast a ring of fire around a target, DO NOT MOVE during this time, or you'll trigger an AoE explosion hitting the raid for 4000 damage.
Furthermore he will occasionally draw the raid to him, cast Mass Slow (dispellable) and start casting Arcane Explosion, move away as far as you can to avoid being hit.
Lastly, at 40% HP, Aran will summon 4 Water Elementals which CAN be tanked, and should be killed fast.
If Aran goes OOM before you kill him, he will Mass Polymorph the raid and sit down for a drink.
All of his spells can be interupted.
If you don't kill him in 15 minutes he will call Shadows of Aran and cause a wipe.
"Who are you? What do you want?! Stay away from me!"

Netherspite
This is an optional boss.
Currently bugged and just Tank n Spank, will be updated when fixed.

Chess Event
This is a required boss.
Currently bugged and not available, will be updated when it's fixed

Prince Malchezaar
Final boss in Karazhan.
The Prince Malchezaar encounter consists of 3 phases:
During the first, he will summon stationary Infernals which do an aoe which should be avoided, also he will enfeeble, reducing player health to 1 and will proceed to cast Shadow Nova, killing anyone enfeebled in 30y unless it's the tank, also causes a knockback.
In phase 2, he will draw out his axes, causing more damage in melee, enfeebling and infernals are summoned just like phase 1.
In the last phase, his axes will attack a random target for 1 damage per hit, he will no longer enfeeble and infernals will be summoned at a much faster rate. Still casts Shadow Novas.
"Simple fools! Time is the fire in which you'll burn!"

Nightbane
Summoned optional boss, considered the actual final boss by many.
Nightbane can be summoned on the Master's Terrace by using the Blackened Urn
Nightbane has two phases.
During the first phase, the boss is tanked on the ground, Tail Sweeping anyone behind him and breathing fire on anyone in front, only the tank should be in front, with his back to the outer 'wall'.
While on the ground, he will place patches of flame on the ground, do not stand in the aoe (Visual is a little bugged and flames may appear where they aren't, just run around untill the effect fades)
At 75%, 50%, and 25% health, he will enter phase two and take to the sky, during which time he MAY spawn adds whichs have to be killed, if no adds are spawned, just keep DPSing him if you can. Phase two lasts approximately 45 to 60 seconds.

Although I listed bosses as required and optional, a Karazhan raid is not complete untill they are all dead! :3

Thank ya very much Eir. Much appreciated.

Nice guide!

Can't wait to see others =p *if you want to of course*
It would help on raids to be able to just read this guide rather than tell everyone at all the bosses....