Boss is a quite general phrase used for several special types of mobs. The following boss types exist:
- Instance boss
- Outdoor boss
- Faction leaders in cities
- Depending on usage, some players may refer to all named mobs, including non-elites, as bosses, as many of these were elite in earlier stages of the game.
A common characteristic for all bosses is that they have a unique name and appear only once in the game. Bosses are harder to kill than the "normal" elite mob of the same level, and almost all bosses are immune to Crowd Control, though some may be susceptible in accordance with their intended mechanics (such as Roar in Karazhan for example).
Bosses are usually divided into three classes of difficulty:
- normal boss
- skull type boss
The normal bosses are the most common variety. Every instance features several bosses (usually 3-5 for a 5 man instance). Normal bosses typically have special abilities that require a unique set of tactics to overcome.
Mini-bosses are usually found only in instances. Good examples are Gatewatcher Gyro-Kill and Gatewatcher Iron-Hand in the Mechanar - they both hit hard and need a concentrated effort of the party, but are still not as dangerous as a real boss. Minibosses, while tougher than normal elites, don't have the complex special abilities that regular bosses do. They usually have smaller loot tables than other bosses.
Skull type bosses are the hardest mobs to kill in WoW. Their level is not displayed as a number, but as a death's head sign. When hovering your mouse over such a mob, the tooltip will read "Level ?? (Boss)".
These bosses have a "dynamic" level - when a numeric level is required for some calculation, they are considered to be 3 levels above the player character involved in that calculation. That is, if both a level 60 warrior and a level 65 druid both tank the same skull type boss, the boss will make crushing blows on the warrior as if it was 63, and on the druid as if it was 68. Similarly, the boss will resist their respective powers as a 63- and 68-level creature would. The first skull type boss that a player may fight with in PvE used to be Pyroguard Emberseer in Upper Blackrock Spire, but as of Patch 3.3.0 this mob is now an ordinary level 60 Elite; The Beast in the same dungeon is still a skull boss, however. There are also some skull type bosses that a usual player can not fight with, e. g. Nessy in the Deeprun Tram.
There is some evidence that with the Patch 3.0.2 changes certain skull-type bosses, such as King Varian Wrynn and the Northrender's Training Dummy are in many ways considered level 83 mobs. Level 70 players have observed that they do far less damage and hit very infrequently compared to what would be expected for their gear, and Crushing Blows (which can now only be inflicted by a monster 4 or more levels higher than you) have been reported.
Similarly, there are reports that old world skull-type bosses behave like level 63 mobs even when attacked by a level 80 player. The very high incidence of spell misses from these bosses, when casting spells against the player, is consistent with a mob that is considerably lower level than the player is.
The culmination of PvE are the raid level boss fights. Bosses in 5-man instances can be very tough and challenging, and may cause many wipes, but the raid bosses are designed to be a real challenge. They may take several evenings to learn, some may appear to be impossible to kill at first. Coordination and discipline of the whole raid are required, frequently one error by the least of the raid members may immediately cause a wipe. Many boss fights consist of different phases, where raid members have to pay attention to different aspects of the fight.
There are three archetypes of boss fights:
Raids must develop an understanding of these three types, and players must be aware not to confuse one with the other. Particularly the difference between a battle for survival and a DPS race is sometimes small. Still it's an important difference whether the damage dealers should put their priority on killing the boss, or on their own survival. Of course, whenever this question comes up, the answer is always "survival first", because dead = 0 DPS, but that insight seems sometimes hard to learn.