Every character needs a resource to perform their abilities. For most of classes, this is mana. Some players will simply refer to all these resources as mana. However, Rogues use energy and Warriors build rage which use slightly different mechanics. The common thing between energy and rage is that they are used to perform abilities.
Except Rogues and Warriors, other classes make use of mana. These classes together called caster. However, Hunters are usually excluded from this list since their abilities are generally not spells.
A mana bar is colored in blue, and the amount of mana a character has grows significantly as they level, just like their health. The total amount of mana a player can have is called their mana pool. 1 point of intellect will increase the mana pool by 15. When a mana user casts a spell, they will use up some amount of mana, and if it is not available, they cannot cast the spell. Because higher ranks of ability have a stronger effect, they also consume more mana. Using mana wisely is important since it is difficult to regain, at least while in combat.
As time goes on, Mana Regeneration allows a player to recover some mana. A caster's natural mana regeneration is tied to their spirit. However, any time ability is used that consumes mana, it triggers the "5 second rule" that prevents any regeneration for the next 5 seconds. This means that if a player is casting spell after spell without pause, they will probably regenerate no mana during this time period.
The attribute "mana per 5 seconds" will continue to operate. Although MP5 tends not to be quite as strong, it is considered vital by many casters at higher levels.
Through drinking is the other common method of regaining mana, which can be done out of combat. Druids use mana, except when in cat form or bear form.
Rogues and Druids in cat form use a different system. They usually start with 100 energy, when they use the ability, it takes a chunk out of the energy bar, and every 2 seconds they get 20 points back. The energy cost for their abilities do not increase with rank which means that while a Rogue can not constantly pour out attacks one after another like a mana user can, they do not have to worry about running out of mana either, and steadily generate energy to perform abilities till the end of a battle, no matter the length.
Many Rogues form complex systems of how they open their battles to use their initial 100 points of energy in the most optimal manner. Many talents reduce energy costs or increase energy generation to make them more effective.
The Warrior's rage behaves very differently. While it is still spent on the use of abilities, the means of gaining rage are unique.
By default energy and mana tend to fill up when not being used. Rage gradually depletes when it isn't being used and Warriors often begin a battle with no rage whatsoever. However, every time a Warrior attacks or is attacked, they gain a few points of rage, to a maximum of 100.
Warriors have a few abilities that add to rage and certain abilities that can be used without any. Charge will reach 15 rage when used to begin a battle, and Bloodrage grants the Warrior several points of rage, and can be used out of combat. Also, because rage tends to build up more slowly than energy, the cost of Warrior abilities is generally much lower.
Unused rage will remain in the Warrior's pool until it is used or combat ends. At the end of combat, rage gradually dwindles. But the side effect of rage is that it is nearly or entirely lost when changing stances is the side effect for rage. In a particular stance, most of battles will be fought which makes it prohibitive to switch from defensive stance to berserker stance to intercept a target that has run away and switch back to defensive.