Enrage is a collective term for boss and other monster abilities which dramatically increase damage output. Many bosses have a hard berserk timer to limit the possible length of the encounter, while others may have a soft berserk that gradually increases tank and healer stress over the course of a fight. Certain mobs and players also have Enrage effects that Rogues, Druids, and Hunters can dispel.
The various types of Enrage mechanics can be classified as follows:
Berserk (hard)
A hard berserk is designed to wipe a group if the boss is not defeated in a certain length of time. Without such a mechanic, killing a boss would just be a question of having enough healers who don't run out of mana. It adds some urgency to the encounter, makes DPS a more critical role, and prevents undergeared raids from killing the boss. Not all bosses have what is often called a 'zerk timer; bosses without one usually use a soft mechanic instead.
The absolute time limit that a hard berserk represents varies by encounter, although most bosses are in the 5-10 minute range. When the enrage occurs, the boss' damage output will increase greatly and the boss will begin annihilating players one by one, starting with tanks and proceeding to the best DPS without an aggro dump. The fight is no longer winnable at that point unless the boss is already very close to death. Any sort of area-effect attack combined with Berserk spells immediate defeat for the players.
Boss goes into a berserker rage! is a common raid warning issued when this time limit is reached.
Examples:
- Archavon, Emalon, and Argaloth feature short 'zerk timers to keep them from being complete tank and spank fights.
- Blood-Queen Lana'thel: Goes Berserk after 5 minutes and 30 seconds. After her initial bite target, players must infect each other with a vampirism (de)buff to do the required damage to her.
- Halfus Wyrmbreaker: After 6 minutes he goes Berserk. Overcoming this time limit is part of the fight, as appropriately geared players are not capable of doing enough damage in the given time without the stacking debuff from defeating the drakes.
Berserk (soft)
A soft berserk is the informal name for a variety of mechanics that gradually increase the difficulty of an encounter and eventually wipe groups who cannot defeat the boss. Soft berserks take many forms. Some are over the entire fight, while others are invoked at a fixed point in an encounter (for example, at a certain boss health percentage, or after a certain amount of time), and some become apparent only when the group makes mistakes or doesn't control elements of the fight (for example, letting adds or stacking debuffs get out of control).
Damage increase examples:
- Gruul the Dragonkiller: Gains +15% damage every 30 seconds of the fight, limiting the fight length to how long the raid's tanks can avoid being one-shotted.
- Toravon: Applies a stacking +25% Frost damage debuff on all players after every wave of adds.
- Bloodlord Mandokir: Levels up every time he kills a player, increasing his damage.
- Deathbringer Saurfang: Uses Mark of the Fallen Champion at 100 Runic Power, which adds significant damage to one target and increases his RP generation speed.
- Cho'gall: In the final phase he gains Corruption of the Old God, increasing corruption stacks raid-wide and eventually wiping the raid.
- Beth'tilac: Gains +5% damage every few seconds of phase 2, which causes her AoE to quickly overtake healer thoroughput.
- Majordomo Staghelm: Two stacking buff mechanics, one increasing the damage of his special attacks every time he changes form and the other increasing their frequency the longer he remains in one form. He should be kept in one form until the special attacks become unmanageable, otherwise the damage buff will stack too quickly.
Other examples:
- Vaelastrasz: The first great DPS race of World of Warcraft. Players have three minutes to defeat Vael before their buff fades and healers no longer have infinite mana to keep up with constant heavy raidwide damage. Compounding this limit, a random player is lost to Burning Adrenaline every 15 seconds, lowering raid DPS over the duration of the fight.
- Chimaeron: Phase 2 reduces all healing effects by 99%, forcing healers to help the remaining DPS finish the boss off quickly.
- Ascendant Council: Ice patches continuously form on the ground in the last phase and will eventually overrun the room, wiping the raid.
Frenzy (hard)
Hard frenzies take the form of large damage buffs, are usually triggered when a boss reaches a certain (low) percentage of health, and last until the boss is defeated. This part of the fight puts immediate stress on tanks and healers, and is almost always the ideal time to use Bloodlust or similar effects.
Examples:
- Huhuran: Frenzies at 30% health in perhaps the most infamous example. In addition to hitting tanks harder, her colossal Nature AoE can no longer be tranqed and must be absorbed for the remainder of the fight.
- Patchwerk: Frenzies at 5% health, surprising tanks who used cooldowns earlier.
- Shannox: Frenzies when each of his two hounds is killed, increasing his damage and attack speed by 30% each time. The first application occurs early in the fight and is not too threatening; the second is fairly serious but must occur before Shannox reaches 30%, as living adds at that point receive a enormous frenzy effect of their own that will cause a wipe.
Frenzy (soft)
Soft frenzies are a damage buff that can be dispelled with a Rogue's 
[Shiv], a Hunter's 
[Tranquilizing Shot] or a Druid's 
[Soothe]. These are similar to other boss enrages, but are short duration and can usually be healed through.
Examples:
- Magmadar, Flamegor, Chromaggus, Huhuran, Gluth: The 'tranq fights' of Vanilla, requiring multiple Hunters to coordinate their Tranquilizing Shot cooldowns. Unlike later soft frenzies, these buffs had to be tranqed off immediately as a few seconds of the damage increase was enough to kill progressing tanks. Some of these bosses also gained raidwide AoE capability while enraged.
- Halazzi: Frenzies in phase 1, increasing attack speed and damage.
- Saviana Ragefire: Frenzies every so often, increasing her attack speed by 150% and periodically casting Fire Nova for 10 seconds.
- Icehowl: If he hits someone during Massive Crash, he goes into a Frothing Rage, increasing physical damage and attack speed by 50% for 15 seconds.
Bosses without Enrages
Although many raid boss encounters feature some sort of time limit, some do not.
Examples:
- Heigan the Unclean: Even during Tier 7 progression, a tank and healer could survive his damage indefinitely if all DPS died in the dance. Fights lasting over 30 minutes have been reported for this boss.
External links
[1] Berserk (hard) [2] Berserk (hard)