Mana is the energy that fuels all active powers in Regnum Online. It can be seen as a blue bar underneath the health bar in the game interface. Running out of mana does not have any direct penalty, but the player must wait until it recharges sufficiently before using powers again.
Under normal circumstances, mana can only be reduced through the use of one's own powers. Mages and barbarians, however, have the ability to directly attack the mana bar of an enemy. For mages, the powers Energy Borrow and Sadistic Servants both steal mana from an enemy and add it to their own supply, while the powers Mana Burn and Evendim's Fury turn enemy mana into damage. Barbarians can strip away a percentage of the mana bar with the power Rend.
mana points = level x 18 + intelligence x 9 - 80
So for example, a level 35 conjurer with intelligence at 69 will have:
35 x 18 + 69 x 9 - 80 = 1171 mana points
Or a level 17 knight with intelligence at 33 will have:
17 x 18 + 33 x 9 - 80 = 523 mana points
Naturally mages, with intelligence as their primary attribute, are the class with the largest mana pools, with archers second and warriors having the smallest. Mages and archers are also able to increase their mana with passive powers: for mages Dragon's Blood increases intelligence and Mana Pool increases theire total mana; for archers Wits increases their intelligence.
The speed at which a characters mana regenerates is determined by the size of their mana pool. In normal (non-combat) mode, mana regenerates at 0.8% of the mana pool per second. So a character with a mana pool of 1000 will have a mana regen of 8 mana per second, a character with 2000 mana: 16 mana per second etc. It is commonly believed that mana regeneration is goverened by the character's intelligence; however intelligence only indirectly increases mana regen by increasing the character's mana pool in the first place.
In battle, mages can regen their mana quickly using the power Ambitious Sacrifice, as well as the mana-stealing spells mentioned above. Other classes have no mana regeneration spells, so as well as their natural regen they have to rely on mages to give them mana with the powers Synergy Bond and Mana Communion.