The runes they inscribe on their weapons are their mana pool (of a sort). As they use their abilities, the runes will be exhausted. After a period of time the runes will refresh. So, they don't have a traditional type of mana pool. You'll most likely see some screenshots of it, but the Death Knight (at current) has three different types of runes that they can inscribe on their weapon: Blood, Frost, and Unholy. Runes can only be inscribed out of combat ( all of this is subject to change as development continues.)

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