This may seem strange - Surely if there are more people then mistakes can be 'carried' by the rest of the group. Well, sometimes. Let's look at an example raid to Zul Gurub, about to take on the first boss, Venoxis. The raid is not fully kitted out with epic items, and it's one of their first runs in to ZG.
Party 1
Warrior (Main Tank)
Priest (Main Healer)
Warlock (Stamina Buff, Raid Leader)
Paladin (Holy, Armour Buff, Support Healer)
Hunter (Nature Res, Main Puller)
Party 2
Warrior (MT2)
Druid (Resto)
Paladin
Mage
Hunter
Party 3
Warrior
Druid (Feral)
Mage
Paladin
Rogue
Party 4
Druid (Feral)
Rogue
Rogue
Hunter
Hunter
As you can see, the first two parties look pretty much like a 5-man party. These groups offer maximum protection to the Main Tank and Main Healer, and the backup tank/healer. You'll notice that Party 4 has little in the way of healing ability. This raid is slightly unbalanced, with slightly weak healing ability and high damage potential. (Lack of healers - familiar problem anyone?). However, looking at Party 4 you can see that each individual member is more-or-less capable of looking after themselves in an emergency - Rogues Vanish, Hunters can Feign Death, the Druid can self-heal without having to worry too much about the others.
A brief discussion of the Venoxis fight. The boss has four large snakes as guardians. At 50% Venoxis turns from humanoid form into a big scary snake, easily capable of dispatching a cloth, leather or mail wearing character in one hit. (Yes, one hit. We're talking 10,000 damage here). In addition, the snake does massive AoE Nature damage. Additionally, Venoxis has the ability to heal, although this can be dispelled. When the snakes are killed, Venoxis gets stronger.
So, how does the group above tackle this?
The accepted tactic is to kill two of the snakes and control the other two, dispatching them after Venoxis has been dealt with. Before the fight commences, a druid and a mage are each assigned a snake. It is their job to keep their snake sheeped or sleeped until the end of the fight. The non-Main Tank Warriors each target one of the remaining snakes - they will tank them until killed. The Main Tank is placed over to a side, with one rogue stealthed beside him. The rogue will provide additional dps to the warrior - all other attacks on Venoxis are to be ranged only.
The fight begins with the Main Puller pulling Venoxis to the Main Tank. The mage and druid control their snake, the other warriors charge theirs. The rogue attacks Venoxis while the rest of the raid deals with the first two snakes in the appointed order.
With the snakes dead, the raid focuses all ranged damage on the boss. The druid and mages keep their snakes under control. At 50% health, Venoxis turns into snake form. The rogue Sprints to safelty, leaving just the Main Tank in melee with Venoxis.
The Main Tank keeps the boss moving (to keep out of the AoE) while the ranged damage continues. Healers from Parties 2, 3, 4 assist in healing the main tank. Eventually, Venoxis dies. The remaining snakes are picked up by the other two tanks, and dealt with.
Sounds complicated, huh?
Well, it is. But if you break it down into each individual's responsibilities, it's pretty straightforward. Looking at it from any single player's perspective, there's a simple job to be done. But a mistake in one of many of these jobs can lead to disaster.
Looking at some possible mistakes:
Someone accidentally wakes up/forgets to control a snake: The healers will have huge aggro by this stage - and in this raid a dead healer is disaster.
Main tank fails to keep aggro or over-damage by a ranged attacker on Venoxis: If the Main Tank loses aggro, all hell can break loose. The one who over-aggroed will likely die as there is no healing to spare, and Venoxis will then work her way down her aggro list until the the raid is wiped.
Missed heal: If the Main Tank dies, see above. It is possible for the backup tank to take over, however, s/he will not be as well-prepared for this job, and the healers will take a few seconds to adjust their healing target. In this situation all damage to the boss must cease while the new tank gains aggro. A wipe, however, is likely.
Missed dispel: If Venoxis gets off a big heal, its back to square one with low mana reserves. This usually means a wipe, too.
Essentially, the power of the raid-bosses leaves little margin for error. As long as everyone concentrates, does their job, these things are do-able. But lapses can be fatal.
There is, however, no substitute for experience. Think back to when you started playing - a 5-man run would have seemed complicated and difficult. This is much the same. The only way to get good at these is to learn, to make mistakes, to wipe half-a-dozen times on the same boss, until finally - it's done right.
And have fun in the process
PS... Oh and wait till you hear about Jeklik. Imagine fighting a winged boss, having dealth with waves of several bat reinforcements, and now fighting with bat-riders circling overhead dropping firebombs left-right and centre. That one's fun too. And pretty damn intense!
'Course, then there's the Lava Surgers in Molten Core. These things like to charge through the raid, knocking everyone flying through the air. Did I mention you get to fight one standing on a narrow bridge above a river of molten lava?
Or perhaps you fancy taking on wave after wave of armoured insect soldiers, one after the other...
